Gimp (at least the more recent versions, and in slightly different ways in the older versions) can do all sorts of things with pressure and line type with brushes, but unless you're using a tablet with pressure/angle sensitivity, they're mostly invisible and unusable, afaik. You can set them to work based on speed or a random variation instead of pressure if you don't have a tablet, but I've never gotten very good results with that.

The tool they work best and most fluidly with is the ink tool (which in newer versions is the icon of the ink pot, before that was a pen nib); with other tools, pressing the + next to "brush dynamics" gets you the menus.


...as for color correction, as far as I can tell, that's just not as good on gimp as photoshop. I spent ages trying to find a way to erase blueline that worked as well as the photoshop methods do, and finally decided there just wasn't one.