Every color has a specific name, as I recently learned that the Dutch flag is, according to professional terms, not simply red, white, blue but existing out of different names of the colors, with an exception of white. Though I cannot remember what the "red" was originally called, if I'm not mistaking, blue was named 'Marine Blue', but I admit that I didn't pay much attention to it when I heard it and gave it no real thought afterwards.
That many people aren't familiar with the many different names of colors is no shame. Calling something 'Light blue' or 'Dark red' is just fine too, as long as you indicate a bit of what you mean. Saying something like 'My favorite color is the green color of my pants' doesn't really specify what you mean. But I asume that everyone got my point with it. =)
As for me saying 'Royal Blue', I just happened to remember it from my time at Pgamers.