Technically "pale" refers to the saturation of the color, and "light/dark" refers to luminance, or the perceived brightness.
In AmE usage however, light can also mean a color that is not intense. I can't think of an instance where pale could be used for a color that is intense but light (or bright).
As I mentioned in my comment, in general conversation, you can use pale or light interchangeably when referring to a color and be understood. If the register is more formal and you're writing for a UK English audience, you should follow the advice in your book just to be certain your phrasing won't seem odd.
For each of the examples below, I went to DuckDuckGo.com and searched for images that matched the term. I had success with each color except for pale dark green - I ended up searching for "pale dark green" fabric to find an image where the color filled the frame. I picked from the first few results the ones I felt were distinct enough to show the difference. There is not a definite line where we can say "this green is pale to everyone who looks at it". Click on the image to see the original sized image.
This is both a light green and a pale green:
This is a light green but not a pale green:
This is bright green (both light in luminance and intense in color):
This is a pale dark green (might also be called gray-green):
This is a dark green (not pale This color is often called emerald or emerald green):