The symbol y has the selected color.

{ColorSetter[Dynamic[y]], Dynamic[y]}

Pick a color, then

y // InputForm
(* RGBColor[0.13130388342107271, 0.9996948195620661, 0.023590447852292667] *)

ColorConvert[y, "HSB"] // InputForm
(* Hue[0.3149416123434789, 0.9764023506067313, 0.9996948195620661] *)

Eric, I tried, but I get the same result as before, being a little square in the selected color. If a do :
ColorSetter[Dynamic[x]] x I do not get any numbers, I get the colored square.

I need the values of the color, in RGB, Lab and HSB, so for e.g. for Red , something like :

{1,0,0} for RGB {0.7,50,50} for Lab {0,0.6,0.8} for HSB

From there on, I can extract the 'Hue' or any other parameter for the selected color.

PS. There are two more answeres in the list. One by Rohit Namjoshi and another by you. They both seem empty to me. Is that correct? I still do not feel very comfortable with how to interact with the Wolfram Forum. Sometimes strange things are manifesting :-)

Notice how Rohit applied InputForm to the variable (or maybe you couldn't see that post). I also like to use FullForm when I want to inspect an expression in detail. Anyway, the little square you're seeing is just the way a Mathematica notebook renders an RGBColor expression in an output cell. I should have realized that this might be throwing you. It's extremely common in a Mathematica notebook for the output to be formatted in some "nice" way. If you evaluate Complex[1,1], for example, you'll see a "nice" representation of that complex number. If you evaluate RGBColor[1,0,0], you'll see a red box. If you evaluate Rule[a,b], you'll see an arrow. But if you apply FullForm to each of these, you'll see that "underneath the covers" they are all just plain old Mathematica expressions with a head and body.

Okay, let's break this down into different tasks.

Manipulating and inspecting expressions

Generally, expressions have a head and a body. You can create them on the fly: Abc[1,"alpha",xyz]. If you type that in and evaluate, the output will look just the same, because there are no rewrite rules associated with the symbols, and so nothing gets evaluated/simplfied/rewritten. The head here is Abc and the stuff between the square brackets is the body (but just think of it as more subexpressions).

You can inspect/transform an expression with these functions:

• Head - tells you the head :). Try it on your variable x when it's assigned a color value.
• Part - extracts a subexpression at a location. So, if x = RGBColor[.1,.3,.5], then x[[2]] will give you .3. ([[]] is syntactic sugar for Part).
• Most, Rest, Take, Drop. Just read the documentation or play with them.
• FullForm, InputForm, TreeForm, etc. There are several *Form functions. Again, perusing the documentation would be easier than me trying to explain.
• Apply. This one replaces the head. yadda yadda documentation yadda yadda.

Okay, so to answer your specific question about extracting one element from a Hue expression, the simplest is to use Part:

x = Hue[0.5, 0.6, 0.4];
x[[1]]

This should output .5. You could have assigned that to a new variable, of course.

You also asked about transforming it to a list. For that, you can use Apply:

x = Hue[0.5, 0.6, 0.4];
List @@ x

This should ouput {.5, .6, .4}.

Using Dynamic

Dynamic caused the notebook to automatically display/use the current value of the expression inside it. So, if you evaluate Dynamic[x] and then elsewhere in your notebook play around with x=1, x=2, x=<whatever you want>, what should happen is that the ouput cell from where the Dynamic was evaluated will automatically update and display the new value.

ColorSetter

ColorSetter is a special function that creates a color picker widget in the notebook. If you give it a value, then that will be the initial value/color that displays in the color picker widget. Try it with ColorSetter[Green]. Now try it with an undefined symbol, like abc. ColorSetter doesn't know what to do with such an expression, so it just returns a raw expression. Now try it with abc wrapped in Dynamic: ColorSetter[Dynamic[abc]]. ColorSetter handles Dynamic expressions by setting the value of the wrapped variable. If abc was undefined before you evaluated ColorSetter[Dynamic[abc]], then the value displayed by the color picker widget is the default (Black), and abc will be assigned the value of Black.

Okay, so try this:

• Restart Mathematica fresh (just a simple way to clean out any definitions you might have already).

• Enter and evaluate this expression:

  ColorSetter[Dynamic[x]]
  

• In a different cell, enter and evaluate this expression:

  Dynamic[{x, FullForm[x], ColorConvert[x, "HSB"], 
    FullForm[ColorConvert[x, "HSB"]], List @@ ColorConvert[x, "HSB"], 
    ColorConvert[x, "HSB"][[1]]}]
  

• Now, click on the color picker that was generated by the first input. Choose a color and tap Okay.

If you play around with this, you should start to see how this works. Hopefully one of these expressions will be the one you want (or close enough to get you pointed in the right direction)

Thanks a lot Eric, fopr your detailed explanation. I will study it tomorrow, but i noticed already that

**List@@x** works fine.

I really appreciate help like yours, as it is sometimes hard to get one's fingers behind a certain concept. Once the concept becomes clear, other applications of it will come easier.

I will get back to you tomorrow.

I seem to have troubles to attach the NoteBook as a seperate file, instead of it being inserted into the post. I managed once, and now I think I do the same, but get different results.

How should I do it correctly?

Thanks. That is the first thing I did and the content of the Nb was somewhere inserted into the Post. Then I used the btn "Add Notebook" at the left top, that inserted the Nb at the end of my post (possibly because I had my insertion point there.

I just tried and now it worked. I must have messed up somewhere :-)

Here's a deeper dive...

Eric, you've put quite some work into helping me :-)

The HueComplement function I get. I had something similar, but less general. Lists : isn't that what is meant with "Listable"? Some functions have that attribute, some not.

HueSplit[.99, .07] the Mod nicely wraps the spread around if necessary. Get it.

So this is what overloading means - restricting the input variable to a certain type (Hue).

Eric wrote : Test (Notice how this time I copied the little color square from above directly into this input expression. Mathematica is fine with that.):

I kew this, but it feels very alien to me. I can see that it sometimes might come in handy, but up till now, the opposite has been true for me. But then again, I am probably still thinking Old School :-)

I worked through your excellent example and of course it works, with a much nicer Frame as well :-)

I will need some more time to go nitty gritty on your code and dive again into the docs (Thread and MapAt). Your solution is very elegant.

I noticed that the Dynamic version and the Manipulate version (in one Nb) interfere with each other. probably because of the same Dynamic variable(s).

There is a thing though that I struggle with : I am so much used to 'stay' in the numbers and variables, until all the calculations are done and only then do the 'Translation' to the graphics on screen. F.i. in this case, I would like to add the RGB, HSB and Lab triplets above each color. But I suppose I would have to get the numbers the same way as I did in my primitive try, and convert to the different colorSpaces.

So, I'll get back to you after having studied some more. Thanks

PS. I tried with a different start color for the ColorSetter (not Black), but nothing seemed to work. I guess the wrong syntax, although I tried quite a few.

Thanks again, Eric, for your excellent explanations. Some things I got, others are still a bit mysterious for me, as I do not seem to get them working, like the labels. But I will get it eventually.

Lab is another ColorSpace, that is fortunaltely supported by WL. It is a very usefull ColorSpace which I use a lot in working on my photo's and images. It seperates the luminosity (the L channel) from the color, which are in the a (Magenta versus Green) and the b channel (Yellow versus Blue). This is usefull in many ways and Lab is the ColorSpace to get your colors popping and right. Another advantage is, that Lab is constructed to work in the way we humans see. It also tries to be 'linear' in the steps. Channel L goes from 0-100 and the two color channels a & b go from -100 to 100. Any 'color' with zero in both the color channels is so a neutral. Measuring in Lab values makes it easy to detect color casts where they should not be.

Your help was very kind and most usefull. I have put on my heavy duty shoes, as it seems that the road is still quite long :-)

best, Beat