Color of tab area where there are no tabs

My form allows for resizing and scroll bars, as users may resize the form
window. However, I have made the inital size of the form window large enough
that everything shows and the scroll bar disappears.

The area where the scroll bar would be, if the window is made smaller is a
tan color, as is the color along the top of the tab control, where there
could be more tabs, but aren't.

how do I get these two areas to be the same color as the rest of my form
background?

Thanks!