vBulletin 3.x custom color schemes?

[PinkMilk]

GDK (graphics development kit) are PSD files you can edit in Photoshop/GIMP.

If your not very good at editting images in Photoshop/GIMP you might want to look in the Graphic Sets section, many people over the years have made different color default buttons and icons Green, Dark Red for example.

Alterative option:
You could also go another way which would be installing a style that has many color variations such as CA Serenity that has 7 colors or CA Evo which has 25 colors

This option does mean not using the default style which you mentioned you wanted to use but I thought I would throw this idea out there in case it was something you would be happy to compromise on.