Twenty Thirteen: audio and video post formats have same background-color

[MikeHansenMe]

When you have an audio post then a video post they appear to blend because of the same background-color. We should change one of the post formats to another color to create the separation. See Screenshots

[MikeHansenMe]

Before

[MikeHansenMe]

After

[MikeHansenMe]

Patch changing the bg using color from header image

[sabreuse]

There are other pairs that have the same color scheme (Link and Aside; Standard and Image). I don't see why audio and video should be considered a particularly special case, nor do I see much benefit in creating multiple new color schemes.

[lancewillett]

Discussed a bit more in office hours, IRC today ​log and decided to go with original design intent and color scheme set up by Joen.

[lancewillett]

See also #23818

[lancewillett]

#23818 has a proposed solution from Joen.

[lancewillett]

In [23785] Twenty Thirteen: improve separation between Link and Aside posts, props Joen for starter CSS rules. Fixes #23818 and closes #23707 as related.