By far the easier way to determine if the colors are dark or light or medium is to print them on your printer in black print only, no color. this will render the print in tones of grey. Compare the prints when they are in this grey scale. You can quickly see which ones are too light to be in the dark pile and which ones do not belong in the light pile, etc. This only takes a few minutes and everything becomes very self-evident. This is called reducing the colors to a grey scale and it is what artists do to evaluate their colors.