Android .xml files: Why do predefined colors not work for me?

Question

When I look at misc. Android tutorials and examples when it comes to specifying colors I very often see constants like @color/red or @color/black e

Answer 1

An important part of this that no one else has mentioned is that the reference to the color has to be

@color/black

but the xml file has to be

colors.xml

(note plural in the xml file name but not plural @color)