Youll want to use a plastic safe spray paint. The problem being youll have to seal any haps with painters tape to prevent the paint from drifting into the internals. Obviously do this while the fan is outside the case. Use very light lwft to right sweeps. Do two passes and wait1 hour. Look at the results and look for which areas are lighter. Do another two light passes tilting the can to best hit those uncovered areas. Wait another hour come back repeat.
Use appropriate breathing mask. (Seriously). A rookie mistake is trying to get it all done in one or two passes. They put on too many layers at once or lay it on too thick. If this happens, use simple green to wash off the paint and start over. (Use a paper towel or q tip if the motor is attached). Simple green works well and is non toxic but will wventually weaken plastic if left soaking too long. Most paint ahould come off in 10 minutes if its still relatively fresh.
Painting models is a hobby of mine. Ive used this technique multiple times with great success.
Do not under any vircumstances use it on heatsinks. A lot of aluminum can be anonodized to just about any color you want including pink. In fact some do have a thin layer of anodizing which helps reduce potential corrosion and dirt build up. Thats how black heat sinks are well...black. hot pink example below.
Http://www.anodizeworld.com/red-anodizing-dye.html