Set colour of title bar for active window?

I started using IceWM a couple of days ago and am very impressed with it. Many thanks to those concerned for an excellent application!

I have almost got it set up the way I want it, but a few minor issues remain. Here's the first:

The theme is Nitrogen, downloaded from box-look.org and the gtk theme is oxygen-gtk. How do I set the colour of the active window title bar? At the moment it's a rather dull grey, and indistinguishable from inactive windows.

Thanks.

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