Replaced textures: Why do they look washed out?

#1

I tried creating a test mod replacing the textures for one of the Caparisons with unsplit versions of themselves. The result does not look right, it looks washed out compared to Vanilla.

Vanilla:

DIFF replaced (looks washed out):

DIFF+DDNA+SPEC replaced (clearly there is also a difference in gloss and specular reflection):

Does anyone know why this happens? Is it due to the fact that the dds files are unsplit, and if so, is there a way to resplit them?

#2

are they .dds files? I remember back in the day .dds files could become washed out with 3rd party programs. the new version on GIMP with a .dds plugin seems to not do this