Chroma-jong Rules

This is the “Chroma-jong” ruleset, as designed by me. It’s a partial ruleset that replaces some normal tiles with special tiles (“chroma tiles”), and can be added onto most existing rulesets (e.g., Shuugi House Rules). It’s themed around the concept of limited wildcards (“tile interpretation”).

Special Tiles

This ruleset uses 15 special tiles that replace these normal tiles: . Because those tiles each carry a special color, they are called “chroma tiles” (see images here).

Ruleset

The Gist (TL;DR)

1. each chroma tile (silver, gold, red, prismatic, fern-green, light-siam) grants +1 chip
2. silver are suitless
3. gold can interpret any one tile in the hand as any face after winning (i.e., gold 5 has no ability until after a valid win has been declared).
4. red grants +1 han
5. melds containing blue are considered closed
6. if drawn during riichi:
   • prismatic can be interpreted as any face
   • fern-green can be interpreted as any “green face”:
   • light-siam can be interpreted as any “red face”:
7. the “Rainbow” is a yaku with variable value:
   • 5 chroma tiles: 1-han
   • 6 chroma tiles: 2-han
   • 7 chroma tiles: 3-han
   • 8 or more chroma tiles: yakuman

Clarification

“Face” vs “Chroma”

A tile has a “face” and possibly a “chroma”.

The face of a tile is the base suit+number/wind/dragon of that tile. I.e., and both have the face “5-pin”.

• the “wait” of a tenpai hand are described in faces, unrelated to chromas

The chroma of a tile is the special color of that tile beyond its face (if any). E.g., the chroma of is “red”.

• a tile’s special ability is determined by its chroma, unrelated to its face

“Interpret”

To “interpret a tile as X” is to treat a tile as if it has face X.

• interpreted tiles keep their original chroma (if any).
• multiple players can interpret a tile differently simultaneously.
  • example : a discarded silver tile can simultaneously deal into player A, who interprets it as , and player B, who interprets it as .

Due to the ability to interpret tiles, the following rules are different from regular riichi mahjong rules:

• a hand can have more than 4 tiles of the same face.
  • a hand is still considered tenpai even if it is waiting on a face that it already has 4 or more copies of
• “furiten” is caused by having discarded or skipped on any tile that can complete any interpretation of the current hand
  • example 1: having discarded regular , the player is in furiten with this hand: , where the has silver chroma
  • example 2: having discarded silver , the player is in furiten with this hand:
  • prismatic, fern-green, and light-siam chroma do not cause furiten if discarded before riichi or by other players after riichi. This is because they cannot be interpreted in those scenarios.

Chroma Ability Clarification

1. silver : can be interpreted as any of the face.
2. gold : after winning a hand, before calculating score, each gold tile allows the winner to interpret one tile in the hand as any face. The hand before and after interpretation must both be valid, completed hands with yaku.
   • this is mostly for getting takame and dora. E.g., the winner interprets the in as to get iipeiko.
   • having multiple gold tiles means being able to interpret multiple tiles (e.g., being able to upgrade a sananko into a suuanko).
   • because the player has to win first, this ability doesn’t change the player’s wait, cause the player to be furiten, or change how the player won (tsumo vs ron)
3. melds containing blue still follow all rules of a meld. The only difference is that now the meld is treated as closed for the purpose of determining eligibility for riichi, fu, and yaku.
4. the value of the “Rainbow” yaku changes based on the total number of chroma tiles, not the number of unique chromas.
   • see Rainbow Stats for Nerds

Modifications

If you add or remove chroma tiles, you may want to adjust the value curve of the “Rainbow” yaku.

If you just want to change what ability each chroma has, below are some suggestions.

If you want some chaos, you can randomize which chroma gets which ability every hanchan, etc.

Alternative Chroma Abilities For Number Tiles

For number tiles, I balance their chroma abilities around the red fives in normal rulesets:

• most of the time, an ability translates to around a 1-han increase to the hand, or a slight speed boost to the hand (but not nearly as much boost as a permanent unconditional wildcard).
• its actual value/speed boost can vary based on whether you play around them.
• personally, I dislike any ability that gives a direct han increase without any downside, but I did include a few ideas below.

I ordered the alternatives abilities below by how interesting I think they are.

1. you can interpret this tile as any face in the same suit if you use it complete a chii, pon, or daiminkan meld.
2. a more complex version of the above: when you draw this tile, you can immediately interpret it as any face in the same suit to complete a sequence, triplet, or quad in your hand. If you do, you must open and meld the completed block and designate another player as “the discarder” (marking the interpreted tile same as you would of a corresponding call). The interpret face adds to the furiten pool of “the discarder”.
   • the meld opens your hand (unless it also involves a blue from the base ruleset)
   • you cannot call tsumo in the same turn that you created a sequence/triplet meld (same as when you make a real chii/pon call)
   • the tile has no ability if you don’t interpret it upon drawing it.
3. grants a 0-han yaku
4. after winning, you must choose 1 (in addition to getting +1 chip):
   • -2 han and +1 chip
   • +2 han and -1 chip
   • for the rule maker: you should adjust the tradeoff numbers according to the chip value
5. grants +(X/2) han (rounding up), where X is the number of blocks (sets/pairs) in your hand that uses a terminal/honor.
   • applies to the final interpretation of the hand (after chroma dragons, gold 5, etc.)
   • for a regular hand, this gives at most 3 han (in the case of chinroutou, honroutou, junchan, and chanta)
   • for chiitoi, this gives at most 4 han (if this chroma tile can have a terminal/honor face)
6. grants +X han, where X is the remainder of the sum of the numbers on the number tiles in your hand, divided by 3
   • applies to the final interpretation of the hand (after chroma dragons, gold 5, etc.)
   • e.g., would give +2 han, but would give +0 han.
   • because all triplets and sequences have a sum divisible by 3, X is affected by only the following:
   • the value of the pair (“head”)
   • the value of the kans
   • whether the hand is chiitoi or kokushi - I don’t really like this one because it’s very arbitrary and/or boring to play around

Alternative Chroma Abilities For Dragon Tiles

1. make the light-siam only interpretable as to reduce the memory complexity.

Non-positive Han Count

• a hand with 0-han is worth 0 base points.
• a hand with negative han is worth negative base points.
  • Example: a -2/30 tsumo hand is worth -500/-1000. With 2 honba, it’s worth -300/-800 (assuming each honba is worth 300). In this case, the winning player pays 300 to non-dealers and 800 to the dealer.

Rainbow Stats for Nerds

The value of the “Rainbow” yaku is estimated from a hypergeometric distribution of “drawing X chroma tiles within 31 draws out of a 136-tile wall that contains 15 chroma tiles”.

I picked “31” as the draw size because players draw 30.5 tiles if no calls were made before an exhaustive draw. The real probability is likely similar, because while players can get more chroma tiles from calling discards, the chroma tiles aren’t easily discarded and most “vanilla-ruleset” games also end around 25 draws (12 turns) (according to MajSoul Stats, for Jade games)

Also, being able to draw X chroma tiles is much easier than being able to win with X chroma tiles. As X increases, being able to win with X chroma tiles drawn also gets harder faster than being able to draw X chroma tiles. In fact, reaching 10+ chroma tiles means you have a VERY specific hand. E.g., uses 12 chroma tiles, and this should be the highest number of chroma tiles you can have in 1 hand.

That said, the probability of the aforementioned hypergeometric distribution is as follows:

• P(X≥4)=46.00%. I.e., about 46% of time, a player gets at least 4 chroma tiles out of 31 draws. While winning with 4 chroma tiles is harder, it may be still too common for this to be a yaku.
• P(X≥5)=21.04%. “5” may be a good minimum chroma count for the yaku.
• P(X≥6)=9.148%. Not much to say here.
• P(X≥7)=2.748%. It’s now very hard to get this many chroma tiles, let alone use this many in one hand. However, it’s still a bit easy compared with even the most common yakuman (the probability of suuanko is around 0.05%).
• P(X≥8)=0.626%. Considering how hard it is to fit 8 chroma tiles in one hand, this is worthy of a yakuman. Its real winrate may end up being closer to rarer yakuman like tsuuiiso, which is around 0.005%.

Images

For a guide on creating/buying these customized tiles, see my Tile Customziation Guide.

Customized hand-shuffled tiles (Amos Prime Gear):

Customized tiles as part of an autotable tile set (REXX III BSJ2):

Viable setup (just mark each non-red chroma tile, and use the original red fives as the chroma red fives):