Stop Giving a Fill Color When Using the Line Tool.
My OCD makes me switch the fill color (when using the line tool) to No Color. It would be great if there was no fill color when using the line tool.
David B commented
I disagree with this. A line is just a path, and a path can have a fill. If I later turn the line into a curve, I may want it to have a fill.
If you don't want a line to have a fill, then just ensure the Fill is set to None BEFORE you draw it. Deselect all objects on the page and set the fill to none (or press D to set it to the default, which does the same thing), then draw the line.
Actually, a line should only have a fill colour. Everything else is paradox. A line with a stroke other than 0 and a stroke colour is not a line anymore, it's a rectangle. Unfortunately, when drawing a line, the default fill colour is transparent and you select the stroke colour. Weird!