(start to) explicitly use float for color values

Bug: skia:9012
Change-Id: I13ef8dea81a9d138b557be53b7adf19285fc9fce
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/209810
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
7 files changed