menu: assigning a color to backgroundPalette renders menu unreadable

[VRathore42]

Actual Behavior:

• What is the issue? * When we assign a color (say blue) to backgroundPalette, the text on md-menu is not barely readable.
• What is the expected behavior?The color should either be white or black based on the contrastDefaultColor property.

CodePen (or steps to reproduce the issue): *

• CodePen Demo which shows your issue:http://codepen.io/vrathore42/pen/oLqdxp
• Details: I used the same colors used to define the blue palette and assigned it to customeBlue. I am assigning this pallet to the backgroundPalette property. Since contrastDefaultColor is "light"i would expect the md-menu text to be white. But that's not the case.

Angular Versions: *

• Angular Version:
• Angular Material Version:1.1.0-rc.5

Additional Information:

• Browser Type: * chrome
• Browser Version: * 51.0.2704.103 (64-bit)
• OS: * OS X 10.11.6 (El Capitan)
• Stack Traces: na

[clshortfuse]

Seems like the issue is related to https://github.com/angular/material/blob/master/src/components/menu/menu-theme.scss#L5

I'll investigate more, but it seems like it's not using a contrast color but a hue from the actual background color. I believe, at a glance, I could change that to be {{background-A100-contrast}}

I might actual shelve this until #8872, so I can apply a opacity for the icon automatically as well.