Hi,
On that converted theme, I think the background colors are actually repeating images. Instead of changing "color" you may have to swap out the actual image (usually a vertical line) that would be found in your theme's file structure.
Look in theme_blue_masters > themes > blue_masters > img and replace the background images.
Otherwise you can change the code in your style css file (find it just like the img folder) with an editor like notepad++ so that it calls for a color code of your choice instead of a colored image.
I hope this gives you a starting spot

Adrian
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