rectangle select, lasso, and the magic wand. (work in progress)
magic wand
the magic wand selects by color. a click takes the island you clicked, meaning the connected run of matching pixels around it.
to take every pixel of that color on the layer, connected or not, hold alt and click. on a touch screen, press and hold on the color instead. add shift to fold the result into the selection you already have.
the wand reads the active layer only, so a color that also appears on a layer above or below is left alone.