"I have tube watercolors. For some reason I can't erase the pencil marks that I have put to outline my painting. I have tried several different leads and still can't erase it. Do you have any suggestions?" -- Terese
Once you've painted over pencil, there's a layer of gum arabic over the pencil which can make it hard to remove (particularly with yellow for some reason). One approach is to erase the pencil as much as possible before you start painting, or put as little down initially. A technical pencil with a thin, hard lead helps keep the amount of pencil to a minimum. (A hard pencil is one marked with an H, with a 4H being harder than a 2H. Don't press onto the paper to get a dark mark with a hard pencil, as you may indent the paper.)
Another option to consider is using a watercolor pencil for the drawing, and "erasing" this as you start painting by turning it into paint. A waterbrush is useful for this, though of course a normal brush dipped into clean water or paint dissolves the watercolor pencil too. Remember to allow for this extra color or pigment from the pencil when mixing up the colors you're going to be putting down.
Some watercolorists try not to have any pencil marks showing at all, others embrace it as part of the painting; neither approach is better than the other, it's just a question of personal preference.