Since 15 have all three ribbons:
35-15 = 20 with a blue and green ribbon only
23-15 = 8 with a blue and white ribbon only
31-15 = 16 with a green and white ribbon only.
So then we're gonna find all the dogs who only have one ribbon.
62-15-20-8 = 19 with blue only
65-15-20-16 = 14 with green only
50-15-8-16 = 11 with white only
(I think)