I'm hoping someone can help me with this, do fondant figures color "bleed" onto buttercream?

If you're using a crusting buttercream, then I wouldn't think so.  The only issue is that after a while the fondant would start to sag and melt onto the buttercream, so that might cause the problem, although I'd think you'd have more major concerns than the colour bleeding at that point.

Fondant will react to humidity, heat and moisture and will "bleed" on the butter cream when exposed.