You may not be able to match the color exactly, but you should eliminate these 'spikey bits'. See the transparency page for more information. You can now move the selection area around and the image underneath will remain the same. This is very hard with Paint Shop Pro, but this is an attribute of the type of image you are working with and is very hard even with Adobe Photoshop. Basically, Paint Shop Pro and similar raster-based image editing programs work with all of the pixels of an image stored in memory.
Most effects work at the pixel or color level.
Vector-based image editing programs, on the other hand, store the image as a description, with coordinates and mathematical equations to define how the image looks. This makes vector based images very good at working with the shape of an image, allowing you to create text to paths and other stuff. However, there are many disadvantages to vector-based programs. Some products by Fractal Design are actually incorporating the best features of the two. I recommend Corel Draw or Adobe Illustrator, although these are rather expensive.