Linda, make sure you're saving the image as a png. Jpg is a terrible format and one of the leading causes of dirty pixels. No matter how you save a jpg, it'll have lossy compression meaning that the black background around the entity will become distorted. As well, if you're already saving as png, make sure you're saving specifically as png24. png8 has a cap of 256 colors which could also cause dirty pixels.Edited By: Ulrike Rayne Schultheiss on Year 17 Day 281 15:17
As for specific programs, I personally suggest Krita. However, Gimp and Photoshop work just as well for doing recolors and custom items. Kirta is closer to Photoshop than Gimp in functionality and is free.