It depends a lot on your base complexion, but some people find MT2 without UV tanning gives them a funny grey-yellow colour.

The reason is that there are two types of melanin - the brownish black eumelanin and the reddish yellow pheomelanin. MT2 produces eumelanin, and some people need to tan to produce more pheomelanin to match it for a natural-looking colour. But as I say - it depends. Try it and see. If you start looking grey, ease up on the dose (or stop for a few days altogether), and go sit in the sun.