Can I paint my own propane tank?

Yes but consider these facts:

• Caution is needed when deciding to paint a propane tank or even your small propane cylinder.
• White and silver colors are the most common used by manufacturers for a special reason. 
• These colors reflect more of the suns light/heat than other colors. 
• Dark colors absorb more heat and thereby increase the internal pressure.

Additionally, paint used for propane tanks needs to be able to expand and contract with the walls of your  steel propane tank.