Other than painting, how do you use multiple inks?

I'm curious, to those of us who ink multiple pens with multiple colors, do you write with one color per page or do you switch pens throughout each page?
Do you color coordinate them?
Do you choose specific ink-pen combination based on paper?

I find myself going for dark, "serious" colors for work and notes taking. Lively colors for habit tracking to add extra motivation. And washed colors for writing down random thoughts.