If you want to hack your webhelp output files, then the answer is "yes you can". Edit your whskin_mbars.htm and look for the following:
Change xxxx to the colour of your choice. Note that if you use a background image, you'll have to change that on the line below to:
Just to add on the above answer, everytime you generate the webhelp these settings willl be reset, so you need to change the color properties everytime you generate the webhelp.
Worked perfectly! Thank you!