I'd like to add to this. I was given new armor to replace my lost suit. After I used the dummy to color it, I didn't know about this bug and tried to make a correction with a standard dye. The dye turned my armor to color 0. When I tried to correct it with the dummies in the DM Lounge, the colors would not correct. So it seems using any dye on armor locks that color in place and tje colors would not change even on the dummy's preview.
Not sure if that helps.