Change layer rectangles' colors to shades of green.

Review URL: https://codereview.chromium.org/107593005

Review URL: https://codereview.chromium.org/107593005

git-svn-id: svn://svn.chromium.org/blink/trunk@164331 bbb929c8-8fbe-4397-9dbb-9b2b20218538