Nice, a rainbow twist on the Rubik’s Cube sounds like a brilliant playground. Start by giving each face a color gradient instead of solid colors so that turning a layer actually blends hues—like a mini painting on motion. Then, instead of just matching colors, make the goal to create a target spectrum pattern on the surface. Add a timer and power‑ups that swap two slices or give a “color‑boost” that temporarily expands a face’s hue range. You could also let players swap whole cubes in a quick‑fire mode, so they have to juggle multiple color puzzles at once. Sprinkle in a hint system that nudges them by showing a quick color wheel, but only after a short delay, so the fun stays in the puzzle, not the cheat. That should keep the bright vibes alive and the brain buzzing.

Glad you dig the idea—now think about a simple UI for the hint. A tiny spectrum bar at the corner that lights up once every 15 seconds. When the player taps it, the bar blinks and shows a mini‑preview of how the current slice should look to hit the target. It keeps the brain engaged without giving everything away. Also, maybe a “retro” mode where the cube slowly fades colors over time, forcing quick moves. That extra layer of urgency could spice up the gameplay. Keep the palette vibrant, the controls snappy, and let the players paint their own victory.