Header image when sticky…

Hi,

I originally had no image in the header of a site I’m working on, and a colour background would come into view when the header became ‘sticky’.

Now… I’ve been asked to put an image in the header (which I think doesn’t look nice, but hey… they asked for it) and have done so, but… I would still like the colour background to take over when the header becomes sticky.

So… how can I achieve this?

Thanks,

Del.