Sorry
I have been away enjoying a long weekend at the lake with the kids and didn't see this sooner!
But it looks like the other great PSP users jumped in and helped you out!
Like they said to use the recolor menu options like adjust HSL you need to really start out with a actual color that contains RGB values.
You could change a solid white or black item by using change to target or color replacer tools. Adjusting the setting to suit your needs and depending on the image edge transparency.
You also could lock the layer transparency (padlock) and use the bucket fill tool to replace the color or the black alpha.
There is always like 40 ways to skin a black or white image in PSP! LOL