I too, have been using paint.net for several years however, I have never used it to create logos or uniforms.
It works great for editing images, resizing images, etc.
From my POV, it isn't complex and is pretty user friendly.
Also, if you don't already have it, make sure to pick up color cop.
It is free too, and is great for getting the color code from a image/logo.
http://colorcop.net/
Finally, here is a link to a super good color charts which will be very helpful when picking out colors to use when creating a uniform or logo.
https://en.wikipedia.org/wiki/Lists_of_colors