Encapsulate color into subrun

Change-Id: I0a9a7e4803348f5e24144f355eeaeb7e8857da18
Reviewed-on: https://skia-review.googlesource.com/c/171042
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
4 files changed