Hey... I just checked out your site with the sample work. I'm not sure what program you're using to make them, but when you save them try not to compress them as much. If you use photoshop you can use the save for web option and try out different compression rates and see what it will look like before you save it.
That way you won't get that fuzzy look on the colours... It took me ages to get my saving technique right (many years of trial and error), I still have trouble with transparent backgrounds... but if you persevere your graphics will look even better!!