I like variety and usually use whatever writing tools are available, but I'm partial to black ink for some reason. Perhaps it goes back to the good ol' days of using black pens exclusively!
I do remember the excitement of having colored gel pens as a kid and using them to spruce up my to-do lists (with decorated borders and all). They certainly added a fun twist and made even the dullest tasks seem more enjoyable. And you're right - they help with prioritizing too; visually, it's easier to gauge what needs doing urgently.
These days, I make do with whatever notes app is handy. It's often easier that way, especially when you're rushed - and most of them have colorful themes now, so the fun element is there too! But there's something about physically writing that feels more definitive, don't you think?