Normalize Paste, Remarkup code embed colors

Summary: These currently use different yellows, and more importantly when pygmentized, is hard to read. This lightens up code embeds and pastes.

Test Plan:
Review Diviner docs, Pastes, and normal code embeds.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: tycho.tatitscheff, Korvin

Differential Revision: https://secure.phabricator.com/D14123