Yeah, that kind of thing would take a lot of work. Would need several different sprites, recolors and... yeah, too much work with not enough time. Ah well, I'll just have slime monsters for now. =P
Oh yeah was going to be the main mechanic of a weekend jam, changing colors might have been the easy way to do it. Red you can shoot fire, green acid, ice for blue, white you walkthrough walls. The other idea was a possession mechanic but also tough.
Colors would be easy, the abilities/sprite change would just be quite time consuming. Especially with a possession mechanic. Definitely something for more then a weekend jam.