Make the menu bar in Yosemite opaque
In System Preferences > Accessibility > Display, enable the "Reduce Transparency" option.
(Note, though, that that disables transparency across the whole system; it doesn't seem like it's possible to disable the transparency just for the menu bar anymore.)
In System Preferences > Accessibility > Display, enable the "Increase contrast" option.
Accessibility → Display → Reduce transparency:
