Non-standard Eggheads, part 3

The last egghead oversight isn't a missing animation frame, nor is it actually an egghead. In Sky Sanctuary Zone, when Mecha Sonic pilots the boss contraption from Sonic 1's Green Hill Zone, he actually uses the same exact palette that is used later during his proper boss fight.

When he pilots the boss contraption from Sonic 2's Metropolis Zone, though, he uses a different palette which replaces the red tones used by the wrecking ball with shades of gray, which are useful for drawing the spinning capsules:

Beyond that, there's another difference. In the Metropolis Zone palette, Mecha Sonic is considerably more purple. This suggests a similar process to what happened with Knuckles' palette: first they split the Metropolis Zone boss off into its own palette, and later updated the main palette to be less purple, neglecting to keep the Metropolis palette in sync.

The madness doesn't stop there for Mecha Sonic. In the Blue Sphere results screen, he has yet another palette, which happens to be even less purple than the main one.

However, this palette has a completely different reason for existing. In the Blue Sphere results screen, the same palette is actually used to display both Mecha Sonic and the Sonic & Knuckles logos in the background. The darkest shades of red and blue were thus made less orange-y and purple-y in order to give the logos their strong, primary colors.