This technique is more interesting a subject than colours.
Many colours could be used here, only the author could tell you what colours were used and how.
I see (on my screen),
-Zenithal highlights in White colour
-grey shadows
-some blue (like on the glases),
-red looks like "Gory Red" VGC - you need any cold red,
-some colours of the skintone could be made from this red with white, or any pre-made colour of skin.
-"Oxford Blue" VMC nr. 807
Go to the tutorial from Morsi
(here), and you will understand better why this colour is here and in what place to put it.