The problem is the muzzle flash above. The green have blended with the transparent yellow at the edges that when I remove the green, the "blended green" is included as you can see from the image above.

Any suggestions to completely  remove the green?

Rerender, and save as PNG's.  B ackground remains transparent that way.
DPH

And set your 'render over' to 'black' if you use png. This will give you a nice clean alpha. Otherwise you may get a fringe of color that's hard to remove.

Translucent data is not stored in the alpha of a .png, just the transparent. Your backgrounds must match, for the translucent parts to look right. Black on black is the easiest, but if you use black behind your flash and don't have a black background in your sceen, your flash will have a noticable black edge.
If you want complex translucents data, you will need to add the effect to your sceen.
There may be another way around this in paint, that I am unaware of.

Quote - And set your 'render over' to 'black' if you use png. This will give you a nice clean alpha. Otherwise you may get a fringe of color that's hard to remove.

I didn't get what you mean with this. And I do used a .png on the image above.

So simply put I must render in .png's for now on. Anything bad about using other filetypes like .tif's?