I'm using \setbeamercolor{structure}{fg=cyan!90!cyan} and it works for the top and bottom of the frame.
Now I want to change the background color of the frametitles. I've tried with \setbeamercolor{frametitle}{bg=cyan} but nothing happens. I want a plain color, not a gradient.

I get the following capture of the frame after applying Jesse's answer:



beameruses palettes in its structure; shades of some primary specification with other colours. – Werner Jun 17 '15 at 14:50