Change homepage boxes text color

[renoirb]

As noted by Jen, the text should be black

• http://lists.w3.org/Archives/Public/public-webplatform/2014Jun/0069.html
• http://lists.w3.org/Archives/Public/public-webplatform/2014Jun/0043.html
• http://lists.w3.org/Archives/Public/public-webplatform/2014Nov/0015.html

Subject also came back in this thread:

• https://lists.w3.org/Archives/Public/public-webplatform/2014Dec/0042.html

[renoirb]

Let’s do this while working on webplatform/ops#33