shower back wall - color change

most pix show 2 walls - always looks good with color change / ? is when u can see 3rd wall - ie opposing wall / does not look good if opposing are same color with back different (consistent with bath wall analysis) / ? so does it look good if color is "L" & if so which color should back wall be - black or grey / 1st row shows L looks good where u can see all 3 walls / &which color should niche pick up 1.floor2.opposing wall3.L // think room = 2 L's / grey shower and door / black tub and vanity