Overall the Blue Ajah has the most representation of Sisters with strength greater than 19 while the Gray has the least representation of Sisters with strength greater than 19.

Black Ajah 152 Index
Blue 136 Index
Red 108 Index
White 100 Index
Yellow 100 Index
Brown 84 Index
Green 82 Index
Gray 80 Index

Most of this makes a certain amount of sense when you think about the nature of the various Ajah's ... strength tends to follow political ambitions to certain degree which seems to be a characteristic of the Blue, so no wonder strong women gravitate toward it. Reds, given their function, would seem to need stronger women. Not surprising to see Gray at the lower end since they are more involved in "mundane" worldly functions (along with Browns). The Green ranking lower does strike me as a little strange, but perhaps it's more about mentality than anything with Greens?