To enjoy the puzzles at their most colourful, you may need to adjust your screen brightness and contrast levels. By adjusting contrast, you should be able to distinguish all eleven shades in each bar, particularly the two darkest, J and K (black), and the two lightest, A (white) and B. The underlined shade letter is the pure screen colour - red, blue and green.
The page background should be the natural black of your screen with no pixels lit (i.e. not dark grey) and may need to be adjusted using the screen brightness control.
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