You didn't account for less than 0, so I left the cell blank in that case:
=IF(C11<0,"",IF(AND(C11>=0,C11<=3),"White",IF(AND( C11>=4,C11<=15),"Green",IF(AND(C11>=16,C11<=63),"B lue",IF(AND(C11>=64,C11<=255),"Purple",IF(AND(C11> =256,C11<=1023),"Orange","Yellow":emoji_nose::emoji_nose:
I'm sure there's a...