Despite claiming I'm 'full stack', I've never done much in the design sphere. Everything seemed so complicated. How do I pick fonts? What's a color scheme? I've recently dived in and while it's complicated, it's entirely possible to learn. People I've never met before were willing to spend 30min of their time going through what I'd done and point out where I could improve.
Ask stupid questions* - you'll find many are willing to help out.
I have never felt that a design was included in the idea of a full-stack software engineer. that would be something id mention separately if I had the skill.
I think the increasingly common desire people have to work for themselves leads to full-stack really meaning full-stack. There are few options: 1) work for a company that employs a designer, 2) work for yourself and pay a designer, 3) work for yourself on something with no GUI, and 4) work for yourself and be able to design. Of those, option (4) is the most tenable for working on something of your own that might make some money without requiring a lot of initial investment.
But I do agree with you that on job descriptions, "full-stack" tends to stop at javascript.
It may not be expected, but it's definitely hoped for that you can at least make something that isn't going to make your eyes bleed.
The nice thing is nowadays Bootstrap (maybe with a decent theme like Flat UI or Ace Admin) will get you 90% of the way there. Very basic design knowledge will get you the other 10%, and for anything past that you can hire a designer.
There's 'design' and there's 'graphic artist' - sorry for the semantic distinction. There's a lot of basic design you can get from BS or foundation or whatever, and themes and such that all look nice. Coming up with specific artwork to match it (logos, something beyond just typed fonts, etc) is something I classify more as 'graphic art' work vs 'design'. It maybe be a distinction without much of a difference to some, and maybe there's a better way to phrase it, but it's a moderately important distinction in my head for some reason.
Ask stupid questions* - you'll find many are willing to help out.
*After doing proper research, of course.