John has answered your question, I will tell you that I have come up on a vessel in a congested water way and never saw him (untill I saw the shadow of his hull) because he was displaying the tri-colored mast head lights. When in shore, most of us are looking at deck level. you don't look up thirty, forty, fifty feet in the air when looking for traffic in harbors or near shore.
Courtney is My Hero
If a man is to be obsessed by something, I suppose a boat is as good as anything, perhaps a bit better than most - E.B. White