These aren't your little sister's watercolors. ^_^
Professional watercolors are a lot more versitile 
than most people think. They are fairly thick in 
consistancy, similar to an arcrylic or oil paint. 
They can be used either that way directly (to 
create precise details, like writing on a sign or 
a hard edge on an object) or thinned to varying 
degrees with water (for less precise details, 
like a bush, or color washes, like a sky).

The big bonus of watercolor (compared to oils or 
arcrylics) is that it doesn't stand up off the 
surface of the paper, which allows cels to lay 
flat for filming. Cleanup is also a heck of a lot 
easier.

Many Sharp Smiles,
--Drac