I got this when I did my first couple of jobs. Worked with a spread who told me to cut down on the amount of water when wet trowelling, and thus eliminate any water marks. I told him to mind his own business but secretly took on board what he said. Everything looks much better now  ;Dyeah i no what you mean, when i plaster a wall or ceiling its flat as pancake, but its not the same colour all over, what am i doing wrong.