Support alpha channel in palette (and colormap for indexed images)
Operating System: all
Description of the feature
Basically there is no reason a palette color could not have transparency data, and at the very least PNG has the concept (see #1256 and PNG spec: https://www.w3.org/TR/2003/REC-PNG-20031110/#11tRNS). Also, PNG specific issue: #3911
Palette colors should have an alpha channel as well.
Edited by Bruno