Is it possible to restore the color palettes of the Game Boy Color port of Donkey Kong Country, just like the way people here had restores color palettes in GBA games?
I presume you mean patches like this:
The SNES and GBA have similar colour capabilities - in fact the GBA can use even more colours - but the GBC, despite having the same amount of colours to choose from, can't display enough colours to make it look like the SNES. Also, the GBA "restorations" are modifying existing GBA games, whereas the first two DKL games were not GBC. Of course people have made DX versions of GB games, so it's certainly possible to do it with DKL.
So, in summary, it wouldn't be easy, but it would be possible.