For instance, the square blocks in the slot machine bonus stage have a lot of individual rotations which cut down on the available VRAM, so it's nice that a single set of art is good for three different colors.
Sometimes the art reuse isn't immediately obvious, though. Here are the contents of CRAM during a special stage:
On the left side we can see the colors for the four kinds of spheres, followed by... the same colors? Except for white? This was really confusing, so I tried replacing the duplicate colors with something else. Some green should stand out.
And suddenly it became obvious.