Although lately I’ve been using this multipen: https://www.jetpens.com/Uni-Jetstream-3-Color-Ballpoint-Mult...
It’s nice having 3 colors of ink available, and it’s not that chunky blue thing we had in elementary school.
I got a box of 12 for a few bucks from Amazon, here is the link since it's hard to search by model,
https://www.amazon.com/dp/B0002LD1NK