Hm well with a bit of messing around I came up with this code to handle the WM_ERASEBKGND message:
Although I'm not sure how to be sure the rect that I get for the rich edit window lines up properly...
HDC hdc = GetDC(hwnd);
HBRUSH hbr = CreateSolidBrush(RGB(88,87,104));
Which kind of ties in to a weird problem. When I create my main window I create it with the following styles:
And it looks the way I want when I run it from VS, but when I don't run it from VS, it isn't maximized (still takes up the whole screen,but has a border). So you can move it around, which I don't want.