Why do you think the mentioned "color-centric" image processing operations deserve a specialized file format, rather than building and using a transient index in memory when it is useful? Do you have some special use case in mind?

Any interactive application, for instance, can be expected to render the image to the screen (repeatedly); any GPU use for texture mapping needs pixels sorted by location, regardless of whether pixel values are palette indices or explicit colours; many image processing tasks, like segmentation and drawing, need efficient access to pixels at arbitrary locations or near already processed locations.