Transparency problem...

[Omega]

How do I mix the transparency color with the original color?

[Mysticaloctopus]

Not sure exactly what you mean, so:

If you're using paint or another program that doesn't display transparency properly, sorry but you're stuffed unless you can open the image with another program

If you're using a program that employs layers, like photoshop, then you have two options:
If you have the original, you can just insert a semitransparent layer of whatever colour.
If you do not have the original, open the image in photoshop or something else with layers and a magic wand tool. Select the "transparent" area and delete it. Make a new layer and position it below the image layer. Fill the new layer with whatever colour and use the settings to make the fill partially transparent. Save the image as a .png file with transparency enabled. If all else fails, post the image here and I'll do it for you.

[Omega]

What about with Irfanview?

EDIT: Correction. What about GIMP?!?