I have a .png image that\'s just white-on-transparent, and I\'m wondering if there\'s an easy way to make that green-on-transparent, red-on-transparent, etc so I don\'t need
For a simpler solution that doesn't require pulling in huge libraries and lets you understand what's going on under their hood (and thus gives you greater flexibility), learn how to use WPF Pixel Shaders (google it).
Then you can use something like the multiply shader here: http://rakeshravuri.blogspot.com/2008/08/blending-modes-in-wpf-using.html