Heya. I have a rev710 game in progress that I just got a slinger on. The coloration looks off compared to my other units (or maybe my slingers just like to feel pretty?)
That's deliberate. When I was looking for Slinger artworks, I found that unique English Slinger model that I just had to use. There are a few common Slingers, but England, Russia, and Viking get models that they don't share with any of the other regular art types.
I still do not know what causes that white Slinger bug. I know it is related to the SLINGER_MEDITERRANEAN model, and that it disappears as soon as you encounter any Archer unit (your own or another civ's).