Every cell holds two concentrations, U and V. They diffuse to their neighbours (U twice as fast as V), react by U + 2V → 3V, U is fed in at rate F, and V is removed at rate F + k. The seed picks F and k.
Tap to drop a blot of V. The colours are the 8 q.d colours by V level. The same ?seed= always gives the same run.
LITGray–Scott (Pearson 1993) integrated with Euler steps. Every 200 steps all concentrations must stay inside [0, 1], or the page throws.
AMBERMapping V to the 8 q.d colours is decoration.