[metapost]: How to draw color gradients

Hi,

i'm sure there are several approaches do get a cycle filled with a
gradient. Like a line drawing for-loop changing its color each line,
etc. but i suppose that this is already done by someone who knows what
he's doing and i hope this knowledge prevents me from spending a lot of
time on things i can only do worse :-)

So, does anybody know a package helping me to reach my goal or at least
a few code snipplets for my aim.

Thanks,
Martin

-- 
ASCII - da weiss man, was man hat.