How do I change the color of a brick? I have a uniquely-shaped brick that I would like to make a darker shade of gray (it's currently blue). 


What media is the best in terms of durability for continued use (i.e. re-use, re-configuration)? 
I assume a spray media would work well, is there a particular type of paint to use that would have a harder surface and be less prone to scratching, sticking?
I don't think that spray paint would be very durable.  Even if you used a primer specifically designed for plastic the paint would scratch off fairly easily.  Also, spray paint would add a noticeable amount of thickness to the brick and could interfere when trying to mate the brick up with others.