I'm not very familiar with PSP7, I've used 9 and now X. The only thing I can think of is that maybe there is a texture set on your color fill. That can make it more opaque as well. If you click on the color in your color palette, the properties box appears. On the right hand side you can select texture. If it is selected, you should deselect.
If that's not it, I hope someone else can help you.
