The lack of blue could also be related to the cost of the paint; if these paintings weren't made for a wealthy benefactor it's likely the artist would have been interested in saving money by avoiding more expensive pigments. Remember that pretty Lapis blue cost more than the same weight of gold!

Just a thought. They did look like they had a fairly limited color pallet in the paintings, it might also have been an artistic choice to keep them all in the same or similar colors.