This is a common stamp/series witch 'everyone' have. But, there is more to do if you want to dive deeper. Michel is listing 11 different colors on the 10 pfennig!
But the color looks very much alike at first look, but there are differences. And you need (in my opinion) a color identifier.
Fist I did sort the stamps I did think look alike in grops. Then I started using the color identifier. It's a lot of trying and failing, but fun.
You place the stamp under the color you think looks closest, then you place a grey card over it to block out other distracting colors. Find the place on the stamp with most color and move it so the color correspond with the hole in the 'color'.
My color checker is Michel and is written in German. Therefore you need to know the German color names, or as I have also have a Michel special in English (and German).
Here you can see the 11 different types of the 10 pfennig stamp. But the observant reader will see that some of the stamps have the same color, then how to tell what is what?
You have to use ultraviolet light and then see what color that apers.
See the symbol and color innside the ( )
I have not came this far yet, will have to do this tonight I think. To see the color of the stamp in daylight, use daylight (not in sunlight) or use a lamp with daylight (I have one with K6400)
Pleas comment and correct if I have missed something. This is new ground for me, learning as I go.