If a web developer can use html5, css3 to add colors, tabs, images etc for a website, then what does the web designer do?

Answer 1

web designers tell web developers that how they want the websites to be....
and web developers execute what they want by writing codes..
to be web designer you don't need to know programming language. it's job us to just give ideas

Answer 2

Designer might be used interchangeably with graphic designer of Web content. Think of the designer as someone who makes the puzzle pieces and then the developer puts them together and brings them to life.