I just got the newest version,and am having trouble opening and using the “paint” .tool.
It doesn’t stay open, and I can only seem to get some “solid colors”
Hi there,
so, first, your profile is a little bit outdated. then again, your account is more than a decade old 
you can update it here, it helps us help you.
that being said, could you explain a tad more your problem ?
you click on the bucket icon (or B on your keyboard), the material panel appears on your right I assume. There you should have a small black house showing you the materials currently used in your model, and a menu next to it with all the extra standard materials. It should be pretty much the same overall as 2015.
could you provide a screen recording, or screenshots of what you’re getting maybe ?
this might help, the 2 videos about the paint bucket and material panel
maybe you could point at the moment when it doesn’t work like it’s supposed to ?