I've been reading more category theory as a prerequisite to understanding some more complicated theorems, and for the first time I'm running into arrows that are distinctly colored. Examples include these diagrams from Wikipedia for natural transformations and universal morphisms:
The Wikipedia articles do not readily show me a link to where the coloring for these diagrams is explained, and I have not seen these colored diagrams in the textbook I have been reading for Category theory. Why are these arrows (and objects) colored blue and red? Better yet, (if possible) can someone give me a link/source/textbook that explains this coloring procedure? Thanks in advance.