The Art of Pebble Merge

In most merge games, tier five looks like tier one with a different color. We wanted the climb in Pebble Merge to feel earned — like the stone is actually being finished. That one decision drove the entire art system.

A color ladder you can actually tell apart

The first version had a problem: the bottom four tiers were too close in color to tell apart at a glance. Players couldn't see what they were about to merge. So instead of trusting our eyes, we measured.

We used CIEDE2000, the color-difference formula designed to match how humans really perceive color. The rule we set: any two adjacent tiers must differ by at least 12 units, and the "drop band" (the gap a player sees between the held pebble and the board) by at least 18. Anything below that got recolored until it passed. It turned a vibe into a test we could re-run after every change.

Polish, not just size

Each tier carries a polish value from 0 (rough) to 1 (finished). Low tiers are drawn matte — noisy, uneven edges, a soft diffuse highlight. As polish rises, the stone smooths out, the highlight tightens, and the color deepens. By the upper tiers it reads as a cut gem rather than a rock.

The faceting trick

The big visual leap happens at the top: once polish passes about 0.5, we draw a set of facets — flat triangular cuts lit from a fixed world direction. Faces toward the light brighten; faces away darken. A sharp rim light and a small table reflection sell the "cut gem" read without any 3D model. It is a 2D illusion, but your eye accepts it instantly.

The goal was never realism. It was progression you can feel in two seconds, before you even read the tier name.

Why "progress" matters more than "pretty"

A merge game lives or dies on whether climbing feels good. Pretty art that looks the same at every step undercuts that. By tying the art to a polish curve and a measurable color ladder, we made sure that every merge visibly moves you forward — which is the calm, satisfying loop the whole game is built around.