How do I change the color of a Transparent .PNG file?

I converted some Photoshop .ABR brush files to .PNG files using a nifty little free program, "abrViewer.net." The result was a group of .PNG files in the color black with transparent background.

My question is, can I change the color to other colors in Xara Xtreme Pro 5 and still keep the files transparent? and exactly how do I do this?

Thank you for your answer.