To save myself a lot of hussle I've been sampling color directly from the original images. It worked allright, but when in game the details on the sprites turned out messed up. I'm trying to figure out, what went wrong and how to fix it.
I suspect it is an issue with my color palette, but does this mean that those original flats use wrong palette, since I sampled it directly, or am I missing something completely.
Spoiler!
EDIT:
An incredibly dirty fix is to artificially increase resolution of the sprite by 2 or 4 nearest neighbor, but I wouldn't really want to resort to this.