Well
imagine a pixel, any pixel, well all pixels have a color value and a alpha. Now see photoshop assumes (stupidly) that your using a 2d application. It doesnt really matter all that much in 2d application. But in 3d application it does.
See unkonown to you even completely trasparent pixels have a color, in yoru case its white, you just cant see that in photoshop no matter how hard you try. But when you save out as tif what usually happens is photoshop loads in the image and alpha separately (or usually depends on how you PS is configured! Its either in I know best mode or in a lets cause trouble 99% of other times mode, both of which are bad), you can now see the color channels.
Now you need to PAINT the entire white part with your swimsuit color not white. Then save again it gets inetropretted differently this time. Now see teh 3d app does sometyhing unexpected to pixels.
Appart form alpha it also counts the next pixels value because it need s the value between pixels too so even completely invisible pixels need to carry out the color along, Then to speed up it builds a pyramid so even very far away pixels would be best used with same color