I don't have much notes on the topic, just the basic concept
Basically, if you know the absorbed color, you'll be able to compare the wavelength of light (you know the order of VIBGYOR) . So now, if you know the wavelength order, you'll know the order of energy, which is exactly the opposite of wavelength order. And finally the Delta is proportional to CFSE.
That gives you your answer.
Hope it helped.