Problem curing extremely dry feet?

I take pretty good care of my skin. I’m the type of person that will take a shower or bath, put on baby oil, pat dry, then lotion, then pants and long sleeves to let it soak in for a while. While the rest of my skin is on point, my feet are always a struggle. I use a foot file twice a week and have even done the thing where you put vaseline on your feet (after a shower) and put on thick socks overnight. Nothing works well. After I take the socks off, they are dry and ashen about an hour later. When I take a bath, even after I put lotion on them I can still see them getting ashy. Thirty minutes later, it’s like I never used lotion. They aren’t cracking or anything like you see on those pedegg commercials and whatnot, but skin that even looks dry REALLY bothers me. I don’t know what to do. It’s summer basically and I’d like to be able to wear sandals without worrying about my feet looking like I’ve been playing in flour (I have darker skin, so dryness shows up easily).

For those of you who do not know the perils of ashiness, never heard the term before, or don’t know what it looks like, http://24.media.tumblr.com/79275c2e9cdb145765298d7bde88e27c/tumblr_mhcmirc3Ll1rkqzxyo1_500.png this is what I’m talking about