This photo shows what the leaves look like after a third and then a fourth round of glazing was done. It really does show how glazing produces colors with a depth and complexity that physical mixing of colors simply doesn't produce.
If you want to lighten a section, such as a leaf vein, you can lift off watercolor even if it's dried (see How To Remove Errors in a Watercolor Painting). Use a thin, stiff brush to do it, but avoid scrubbing the paper or you'll damage the fibers. Rather leave the paint to dry then lift off some more.
