Colored cellophane maybe?
Don't use regular cellophane as you will start a fire. You need to get an actual theater light gel. The 100w colored floods get hot. If you want to stick to standard bulbs building a coffee can style enclosure around the light with a gel on the front will be a vast improvement. You can go with the higher efficiency 45w floods that produce about the same amount of lumens.
You could try a high-temp paint but by the time you messed around with that it would be less expensive to buy a colored CFL bulb-less wattage, less heat and better color saturation for $5 at the orange big box store.
Your best option is to dump incan all together and go with DMX controlled RGB LED, you will never go back. We are using 20 this year.