I don't have Photoshop, nor have I ever used it. But just thinking to myself, I'm wondering if it could have something to do with RGB v/s RYB.
For example, in RGB, equal amounts results in White. But in RYB, equal amounts result in Black.
Maya operates in RGB as far as I know. So perhaps you are using RYB in Photoshop and it's messing up when importing into Maya which I don't think understands RYB.
Don't be satisfied with what you can do but rather strive to do the things you can't do!