I mentioned a while back that I have been doing this, and I did take some pictures of what I was playing with, at least. I don't mean to imply that I'm making anything from scratch - rather, I'm mixing moisturizer and foundation to get something halfway in-between in consistency. This is something that I only thought of because it was suggested in the very first Sephora Play box regarding Ole Henricksen Sheer Transformation moisturizer: that you could mix it with your foundation. And I eventually did that, and I liked it. I don't have a picture of the foundation in question, which was L'Oreal True Match - you can find it in any drugstore. And well, obviously I liked it, or I wouldn't have been experimenting with doing it again. (As for the True Match, here's a post from 2013 where I describe how I mixed two colors of True Match to get a custom color, and I'm still doing that. I think I've been doing that since True Match first came out, pretty much.)
So about the time the Ole Henricksen/True Match combination was running out (because it was a very small quantity in the first place), my moisturizer was also running low and I decided to try Origins GinZing. I talked about that at the time, and I mentioned at the bottom that I had mixed the remaining LaFresh with foundation. The LaFresh is Good Day, in the blue jar, and I think I just started out with what was left of my True Match, but it was getting low, and I didn't like the consistency too much (improper moisturizer-to-foundation ratio, I guess?) and so then I got creative. I had a couple of other things that I hadn't been wearing, and I mixed them in too.
I think I am hooked on this concept - at least, now I feel like regular foundation is too heavy, and I was already hooked on moisturizing my skin a lot anyway, so it's useful to me in more than one way. I suppose you'll get different results based on what you use, but both of my experiments came out with sort of a whipping-cream texture to them, only skin-colored, of course. And so far it hasn't separated - you mix it up and it stays mixed, it seems, which is nice. (Only time will tell if it's really going to stay that way, though.)
Added: I think I meant to say this in the first place, and I forgot, but I should point out that one of the reasons this works for me is because my skin has changed. My skin used to be blotchy and prone to breakouts, and the reason that it's improved is probably only partly due to my skincare regimen of moisturize, moisturize, moisturize. Another part is presumably that I'm postmenopausal now. My mother's skin never completely stopped breaking out after menopause, I know, and mine didn't at first either. But my breakouts got fewer and fewer and have finally stopped (knock on wood) - it just took a couple of years. Anyway, the point is, I don't seem to need a heavier foundation nowadays. Thus, all of the above. Of course there are already lighter-weight foundations and tinted moisturizers available, but the mix-your own approach does provide you with a lot of flexibility as far as picking your own foundation (especially the color) and also the moisturizer you like.