How To Tell The Difference Between Shades Of Blue???

I have a GB Scott #55 here and I'm trying to determine the shade. The Scott Standard lists blue and pale blue as the colors for this stamp. However, when I check the Scott Specialized, it lists blue, pale blue, cobalt blue and milky blue. How in the world am I supposed to know the difference? I realize that it's likely a standard blue but what if it was milky blue and had a cat value of $1,600 rather than the blue value of $180? I have a fabulous vintage Stanley Gibbons Stamp Colour Key and I would say it's closer to blue than pale blue but the key does not list milky blue.

Is the only way of being sure to have it appraised by a professional that had verified versions to compare it to? Not that I'm going to do that...

Post a picture. We might be able to help based on a picture.

Well in my case, I don't even have to go that far...I ALWAYS have the cheaper one!

I often have trouble identifying one if it is almost like another and I don't have both side by side. If you can get both on screen, maybe internet pictures will help. If not that your guess is probably better than mine.

Not to mention determining colors on a Stamp 100 years old, colors do tend to change over a long period of time. The best method is always to compare it side by side with a certified example.