Acrylic paint should work.
This looks like a good tutorial:
Hi Car: First of all, you want to make sure your bulb is very clean. Wipe it off with vinegar and then you can use any acrylic paint, on the inside or outside:) Good luck
Hi! ...hope this helps!
Inside or outside?
I have used both acrylic and Testors enamels.
I used sprayed paint on these clear bulbs. https://thriftednest.com/diy-dollar-tree-christmas-ornaments/
Chalk paint works awesome! Or even craft paint.