In addition to the new upgraded forums, we also have an additional theme/skin that allows you to pick your own colors!
It's the IPB Unlimited theme that you can see on the dropdown menu
in the lower left corner of the forum:
If you prefer the original blue IP.Board theme, choose the IPB.Board theme:
I wanted green for mine, so I chose the IPB Ultimate (imported) theme:
Using the IPB Ultimate skin/theme, you just choose the little white paint brush in the right header area below the search and above the Recent posts:
Choose the color range from the verticle color band in middle, then choose the specific color in that range, in the big box to the left in the color picker, then when you like it, click the green checkbox.