This is actually an interesting question that depends a lot on a human perspective and what you define as ‘Generally Blue’ and what’s else is in the container.
I personally would define generally blue as when you have two colours, say red and blue M&Ms, and you reach in the container to pull out 3 you have a 50/50 chance of pulling out three blues. This definition would require that you have 79.58% blue M&Ms in your container.
Honestly this sounds like a bit high to me but probably can be a real bitch, and the test sounds secure to me. Physiological I think 2/3 blue 1/3 red would have most people say it’s generally blue and the ratio would go down as you add other colours. I think 1/2 blue and 1/2 a mix of 4 or more colours people would still say it’s generally blue.