[Combine two images? (the white one indicates the alpha channel of colored one)]

THANK YOU SO MUCH!

[Combine two images? (the white one indicates the alpha channel of colored one)]

So basically what I'm trying to do here (I'm using a game textures), the game reades the _ image and the basic colored image and combine them so that the more white parts are most transparent and the less white (more transparent) white parts indicate to the transparency of the colored image. How  would I be able to do this?