MAC Studio Fix Powder Foundation - C7

So I've been using this powder for a long time now. I want to like it so badly but I'm not sure. I have VERY oily skin so I use this as my foundation. My shade is C7. When at home, applying my makeup under a lamp on my makeup desk, my makeup looks great. Perfect color, well blended, it just looks really good. But when I step outside, something just doesn't feel right. I've been in the car driving to work, pulled down the car mirror in the sun visor and been like "OMGGG this looks terrible", but then I'll get to work and look in the mirror and it will look fine. One day while goofing off at work, I took a picture of myself and was like "OMGGG this looks terrible" but when I went to the bathroom, it looked fine. I just don't know what to make of it. This is the shade that was recommended for me at the MAC store so I'm assuming that it's the right color. And in some lighting it looks great and in other lighting it looks horrendous. I have this problem with all foundation though, whether it be powder, liquid or cream. I haven't had the guts to ask anyone, hey...does my face look ashy or anything? But I really need to know. It's to the point that when I'm in lighting that I know isn't good for me, I'm embarrassed for anyone to look at me. But, like I said, it could just be me and maybe it looks fine. It's pretty expensive but I'm willing to pay for products that work so I need to know whether this is good for me before I run out of this one lol. It hasn't caused any break outs or anything so that's why I really want to stick with it but I just don't know. I'm working up the nerve to ask someone's opinion on it one day.