sync color4f with docs

NOTRY=true
TBR=brianosman@google.com

Docs-Preview: https://skia.org/?cl=156300
Bug: skia:
Change-Id: I7e4f8079b5c30dfaf08cf719a5d90a0eff64906b
Reviewed-on: https://skia-review.googlesource.com/156300
Commit-Queue: Cary Clark <caryclark@skia.org>
Auto-Submit: Cary Clark <caryclark@skia.org>
Reviewed-by: Cary Clark <caryclark@skia.org>
2 files changed