Hi,
i just wanted to colour the missing white elements.. For the element "bridge" select the polygon -> "group select" I could select the individual planes (I even did not had to use your mentioned "split")
But when I want to do the same with element "quadrat" that does not work, I can only select one of the four sides after splitting, but not one of the individual elements, so using the split function is splitting the four sides of the whole quadrat, but does not let me select individual planes... what I am doing wrong?