I've really got to stop mentioning
Chrono Cross in what seems like literally every thread I contribute to, but aside from being my favorite game, it's also one of the most colorful games I've ever seen outside of the
Katamari franchise. Hell, the entire game is based around color. Every character has an innate colored element attribute that opposes the opposite (redundancy much?): black and white, red and blue, green and yellow. Magic is in the form of 'elements', which can be used once per battle per individual piece, and attacking with an enemies opposite element deals greater damage (hit a black innate character with the white element UltraNova, for example, and they're in for a world of hurt). Coupled with meticulously hand drawn backgrounds, I think this is the most visually stunning game released in its generation (for PS1 era, the graphics are superb).
For a visual example, this is the final dungeon of the game, called the Terra Tower -
Or the area called the Dimensional Vortex, with a beautifully rendered, almost crayon-drawn art style -
Colorful and fun, but it also delves into deep philosophical and metaphysical quandaries that went well over my head the first time I played it at age 10, but that I enjoy replaying it now at 21.