Change color of the Cmd+Tab app switcher on Yosemite? Is it possible to change the color (specifically, darken) the cmd+tab application switcher on yosemite?

It's hard to see, especially against a white background:
You can darken the the background of menu bars in Yosemite using "Dark mode".  To enable this go to System Preferences-->General, and check the box next to "Use dark menu bar and Dock".