I use PSP 7.04 and PSP 8.1.

If I render over black, it works fine

Here are some examples of dark and light clothing over black and white to show you the difference. I don't see any pixels around mine.   Maybe it has something to do with the version of PSP you are using. You couldn't pay me to use any PSP version made by Corel.

Example.  Click on the image for a larger view

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi