Change background color?

[h4n5]

Hey there...

i'm using vBB 3.7.0 and i want it to change the background color from post to post within a thread...

example:

Thread
-----------
Post #1 - Background Color Grey

Post #2 - Background Color White

Post #3 - Background Color Grey

-------------------------

i saw this in some vB forums but couldn't work it out :(

would be glad if some1 could help me...