How the difficulty is calibrated — and why that makes it fair

The problem with “it gets harder”

Most color-difference games tune difficulty by feel: shrink a slider value each level and hope it works. But color is not one dimension — a small change in brightness is easy to spot on a yellow tile and nearly invisible on a dark blue one. The same slider step can be a trivial level or an impossible one, depending on the color the game happens to roll.

ΔE: measuring how different two colors look

This game does not tune by feel. Every level places an odd tile at a target difference measured in ΔE76 — the Euclidean distance between two colors in CIE Lab space, the standard approximation of how different two colors look to human vision. The engine converts every color through sRGB → linear RGB → XYZ → Lab, then searches for the smallest offset that reaches the level’s ΔE target.

The result: level 9 is genuinely “a ΔE of about 3 apart”, on every color, every run — so difficulty rises in equal perceptual steps instead of random jumps.

Three safeguards the ΔE number alone can’t give you

1. An 8-bit reality check. Screens mix colors from 256 values per channel. A ΔE target can mathematically succeed while both colors round to the exact same RGB values — a level with no answer. The engine rejects any puzzle where the odd tile and the base tile don’t differ by at least 2 units in at least one RGB channel.
2. A perceptual floor. Differences below ΔE ≈ 1.5 stop testing your eyes and start testing your screen. Levels never go below 1.5 ΔE — after that, the grid size and the timer make it hard.
3. Bounded brightness. Base colors are locked to a mid-lightness band so the offset always has room in both directions. Without this, late levels would occasionally “hit the ceiling” and jump in difficulty.

What this means for your score

A level you fail was verifiably within human reach — most people clear 8–12 levels, trained players 15–20. The ranks from Rookie to Oracle are all measured on the same scale, so your best level is a real, comparable number.