The color of the ink doesn't change. I have a brightly colored oriental dragon chestplate, shoulder, half sleeve and the colors are as bright as they ever were, they look a bit different against my skin when i take mt2. For me though, being italian, i turn a very deep olive color with mt2 so not sure if that has any impact.
I wondered the same thing early on using mt2 so i compared two pics to judge the color of the tats. The color of the tats is the same, the canvas they are on(my skin) has just gotten darker.