Sorry, folks, but I blew it. On my recent review of Cassiopeia I said that only one part of the style was colorable.
I stand corrected.
Here’s what I missed:

See where it says <— Click to switch modes? I completely missed it. There are three settings available: Main Hair: Click on it and it will bring you to All. A final click will take you to Streaks.
Here’s an example, where I colored all three segments differently:

I apologize for the confusion.