Sumif, sumifs, counta, countifs??

I have the following table:

COL A COL B
Blue 5
Red 3
Yellow 2
Green 1
Yellow 1
Red 4
Yellow
Blue 6
Purple 3

I need to count the number of times COL B has a number or data in it (any number it doesn't matter) if COL A has the word Yellow next to it. So in my example above, Yellow would result in 2, Purple 1, Blue 2, etc. I cant work out how to do this, i think it needs some sort of nested SUMIF, COUNTA formula but cant work out what?

Many Thanks