Input is a color, expected return value is an index.

Change-Id: I1bb6977cea5aad7a89082ace12f0a85c58a0f2e3
Reviewed-on: https://gerrit.libreoffice.org/39045Reviewed-by: Tamás Bunth <btomi96@gmail.com>
Tested-by: Tamás Bunth <btomi96@gmail.com>