add stages for black and white colors

histogram of test skps:

black: 1/7
white: 2/7
other: 4/7

Bug: skia:
Change-Id: I3a092899d31ce87837e66e5c8ea9ec5e0f239361
Reviewed-on: https://skia-review.googlesource.com/21408
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Reed <reed@google.com>
14 files changed