Summary:
Seems to be known TODO in the code, but no idea why it
was never solved, especially since tweak is so much easy.
It might be arguable that we need to support painting
color space, but it's still much better to convert to
sRGB space. It's gonna to cover 90% of cases anyway.
Reviewers: campbellbarton, brecht
Reviewed By: brecht
Maniphest Tasks: T37670
Differential Revision: http://developer.blender.org/D65
d3f3fb89cc