Cannot fill image using Paint tool

[RaptorMoonX]

Hello!

I'm using XDPX9 to create logos for my new game company (Gummisaurus Games). I created the dinosaur using the Shape Tool and a lot of patience (I have Cerebral Palsy and it's hard enough!!). All of the outline is connected with no gaps. I want to fill the body with a rainbow color with the Paint tool, but when I try to use it, nothing happens. I have several layers that are locked, but the layer that will hold the fill is visible and unlocked. Why wouldn't it work and what am I doing wrong? Any help would be greatly appreciated. Thank you.