I'm trying to change the colour of my character's hair and I'm running into a bit of an odd problem.  I've saved the diffuse texture, and edited it in Paint.NET.  But when I go to add it in, the hair model seems to lose all its transparency.  For example:

Before:


After:


I'd like to get the texture of the second shot with the softness/blending of the first one.  Is there something I'm missing?