Deep blue = ocean blue Dark blue = navy blue Light blue = sky blue

I'm not sure there's an "official" answer to your question. There are many different ordinary and technical words for describing color. The sea is often described as "deep blue" which may well be a combination of the idea of the ocean being both blue and deep. If I may refer to "brightness" and "saturation," to me a "deep blue" implies something that is very BLUE; that is, highly saturated, very pure, highly blue; while a "dark blue" implies a blue that is dark--closer to black--but not necessary very rich or pure or saturated. At sea level on an ordinary day, the sky is blue, but it is not a deep blue. At 3,000 meters on a dry day without air pollution, the sky is a deep blue. If I am looking at two blue shirts in a clothing store, neither of them may be a very deep blue--they may be a somewhat toned-down, greyish blue; but one of them may be a light blue and the other may be a dark blue. However, I suspect an artist in oil paints, a clothing designer, a graphic designer using Pantone colors, a web designer, etc. might all have different answers. If it helps, this web page http://en.wikipedia.org/wiki/Web_colors show the "official" color names used in the CSS specification. There isn't any "DeepBlue" but you can see for yourself the comparisons between "LightBlue" and "DarkBlue" and between "SkyBlue," "LightSkyBlue," and "DeepSkyBlue."