Before begining your color blocking technique for walls, practice your design ideas on a few sheets of paper (one inch equals one foot). If your wall is 8' high for example, draw on your practice paper a few rectangles 8'' in height by 2'' wide then fill in the rectangles with smaller blocks.
Try and have the top, middle and bottom sections look different from each other. After drawing your shapes on paper, use pencil crayons or felt pens to color in the blocks.