As I'm still in exploration mode with the thought process of a journal and going back through all of my old wanna-be journals I don't really have an answer about pen colors and journaling.

I will say on the whole I prefer black ink. Not blue ink. Black ink. As far as colors go, I'm more likely to create a graphic with various colored text than I am to write with different colors. Guess my brain processes writing and graphics text as two completely different things.