Blends

I know that this is an "icon" tutorial community, but this happens to me with icons and blends...

I get this awful white color between the pictures I want to blend... here there are two examples:

http://i203.photobucket.com/albums/aa268/abby_road87/headers/mtheader1.png

http://i203.photobucket.com/albums/aa268/abby_road87/headers/mtheader6.png

It doesn't matter if they are dark or light pictures, I always get that coloring... If I change the background color I get the color that I've chosen, and it looks really bad.
Can anybody help me? Thanks in advance...