Subtle (or I guess just more technical) distinction to make: the red, green, and blue components of a particular pixel in a normal maps are the "x", "y", and "z

Subtle (or I guess just more technical) distinction to make: the red, green, and blue components of a particular pixel in a normal maps are the "x", "y", and "z" components of the normal vector, where "z" is defined as the tangent to the plane the image is taken from, and x and y are relative to the image. It's basically the same thing, but might help if you're more familiar with vector/matrix math