Weight painting an object In the picture above I have two feet. The blue one is the one I have selected and gone into weight paint mode. I'm trying to change some vertices to red in weight paint mode but don't really understand how to do this. When I use the brush on the foot, nothing happens. It simply remains blue. It also doesn't show me vertices. It appears solid. If I enable wire frame mode, it shows all the vertices but doesn't allow for selecting certain vertices.

How can I paint specific vertices along the seam of my foot red?
In your screenshot the weight and radius of your brush are set to 0, and you are using the subtract brush.

If you set them to higher values and pick a brush like mix, then it should work: