And everyone uses it for a reason: color is one of the primary discriminators of human vision, it carries information efficiently and does it instantly, as clearly laid out in the Wikipedia article about visual search (pop-out effect) : http://en.wikipedia.org/wiki/Visual_search

It seems strange that Rob Pike would call it "infantile". I don't think it's very modern (nor mature) to say that either, since it completely ignores years of research done on the subject by scientists. But then again, to each his/her own.