Two explainers on tomato colour at
https://frogsleapfarm.blogspot.com/2014/04/genetic-control-of-fruit-color-in.html and
http://www.kdcomm.net/~tomato/Tomato/color.html
I cannot recall anything but red tomatoes from my youth. Yellow was dangerously exotic maybe 30 years ago. All that diversity, hiding out of plain sight!