Here's some context for D'Arcy Thompson:

As soon as we adventure on the paths of the physicist, we learn to weigh and to measure, to deal with time and space and mass and their related concepts, and to find more and more our knowledge expressed and our needs satisfied through the concept of number, as in the dreams and visions of Plato and Pythagoras; for modem chemistry would have gladdened the hearts of those great philosophic dreamers. Dreams apart, numerical precision is the very soul of science, and its attainment affords the best, perhaps the only criterion of the truth of theories and the correctness of experiments. So said Sir John Herschel, a hundred years ago; and Kant had said that it was Nature herself, and not the mathematician, who brings mathematics into natural philosophy.

[ETA: Here, p.122, is the context for the reference to Herschel.]

And he goes on to rebuke the life sciences for having been slow to follow the same course. He suspends judgement on whether the mysteries of the mind and consciousness can be solved by physical science, "But of the construction and growth and working of the body, as of all else that is of the earth earthy, physical science is, in my humble opinion, our only teacher and guide."

This seems to imply that we should delegate decision-making to a system that is certain the sky is rgb(0,255,0) over a system that assigns the bulk of its probability to various shades of blue.

I think that is a perverse reading of Carveth Read's maxim.