Issue with Recoloring hair on a Mac

Hey so I'm using S4studio on a mac, everything is up to date. My issue is only with importing alpha hair textures, not clothing. It is the most noticable with light colors. So first, I export a light colored texture from the original alpha package file. It exports as a .png to my desktop. I would go through the whole retexturing process in photoshop and export that as a .png to my desktop. Whenever I re-import those textures, I get a weird backdrop shadow that makes the hair look darker. It almost looks like the textures are being layered on top of each other and it has created some depth to it. In game, it translates to black strands of hair on top of the texture, and makes it look dirty. This happens even if i simply export the texture and reimport it without editing it at all. Really need some help! This is the only reason I really use S4studio.