Metro skins use Metro colors, not glass colors.
Use the color settings in Windows.
On Windows 10, use the Personalization color settings.
On Windows 8.1, skin does not use desktop color. It uses Start Screen colors.
Need to go into Start Screen mode to use the color adjustments there, then switch back to desktop.
Other options
Winaero has a small program that can use the StartScreen color on desktop, or desktop color on start Screen:
http://winaero.com/comment.php?comment.news.217There might be other skins in the Start Menu Skins section,
that look similar to Metro skin, but use glass color.
I was going to say, edit the skin, to use different Metro colors.
It is not so much the color that can be changed, rather the brightness shade of the same color.
It may not be worth the effort?
I'm not a pro here. Hope this helps.