There's been a bit of an Instinct resurgence lately where I am. Probably more than half the gyms I saw today were yellow. It was a nice change.
I have a theory that Blue, as the middle and therefore sort of the default option, picked up a lot of casuals, which helped them dominate in the early going; but numbers're starting to become less of a factor now that more players are deploying Pokemon that are out of reach of casual players' attacks, which makes the relative numbers of serious players more important than just the raw numbers.
In the long run it may even turn out to have helped out yellow to be outnumbered at the start, as that might attract people who are looking for a challenge. But perhaps that's wishful thinking.