Honestly speaking here, if that is you in the avatar, then you are probably not "fair". If we are talking about Fair/Light/Medium/Dark/Deep, I would say you are in the Medium range. What could be happening when you put on your MMU is that it is coming to contact with oil, and that can significantly darken MMU so that it no longer matches.
If anything, it could be that the tone/tint you have been using is pulling a little bit strong for you (like too warm or too brown, etc) and it is a stark contrast on your skin. The brand I like to use is Milan Minerals. That brand is particularly known for having a wide selection of tints that are matched for Light - Deep skin without being too ashy -OR- too strong on the face.