I've designed the below GBC called Rainbow Wave. It has 38 Lego colors and about 1150 moving parts. It is powered by a single motor, with each of the colored pistons sitting on an 8-tooth gear. Each piston’s gear is exactly 1 tooth offset from its neighbors making one wave 8 colors. The GBC is level so the balls are moved by the waving surface.
Free building instruction for version 2 and parts list is available on Rebrickable with a thank you @Courbet for the improvements and creating the digital model! https://rebrickable.com/mocs/MOC-7456/Berthil/rainbow-wave-gbc-v2/