Why is there such a difference between the colors generated out the same image with both color.adobe.com and InDesign's own Color Theme Tool?
After much experimenting, I can only conclude that the Color Theme Tool is far from "matching" color.adobe.com in quality.
I may be missing something obvious, after all this time.
Here's a simple example, an sRGB image I picked the other day on Facebook.
The Document Intent is "Print" ("Web" in the above screen capture), so the Color Theme Tool generates CMYK colors, out of the sRGB image. That's expected.
Granted, color.adobe.com generated themes are encoded in CIE Lab space.
To do a fair comparison, I made sure to "Proof" colors, so that the CIE Lab colors don't overly look "bright" as compared to their InDesign counterpart.
Don't get me wrong, I think the Color Theme Tool is a neat little addition to InDesign's toolbox but, as it stands, according to my limited understanding, it systematically "dumbs down" the colors of ANY image, regardless of the Document Intent (I experimented both ways, Print and Web, tried all the settings in the Color Theme Tool options).
The cherry on the icing, if I may say so, with the implementation on color.adobe.com, is the fact that, upon completion, it's plain to see where the "tool" sampled the colors from, as shown here:
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Here's a fresh, new experiment this morning.
The Document Intent is Web.
I used the Shift key along with the Color Theme Tool to capture this single color in the mad hatter's hat.
I get the 6 harmony rules.
Generated swatches are in RGB space.
For curiosity, I took a sample of the same area with the old Color Picker tool -- see swatch on the right, top.
Why does the color has to be "dumbed-down" from what it is, in the image? Why? Why? Oh why?
It's as though the color *has* to be converted to the Working CMYK space *first", before being converted to RGB.
Jeffrey's suggestion led me to take a closer look at that Mad Hatter image, in Photoshop...
Clearly, the area I'm sampling from with the Color Theme Tool, has suffered heavy JPEG compression (typical 8x8 square pattern).
It makes sense to think that both the regular Color Picker and the Color Theme Tool are NOT sampling a 1x1 pixel area but a larger one from which they must be "averaging" the color. I don't how large it is (5x5% 11x11? 20x20?).
So I selected an area in the Mad Hatter's hat, in Photoshop, and used the Average filter on it, to make sure that, upon "picking" in InDesign, it would have a uniform area to select from.
That resulted in a small improvement in brightness overall -- lesson learned, but still, a far cry from the original RGB color. 
The original Photoshop "area" is RGB 245 119 143.
After sampling with the Color Theme Tool, using the Shift key down, it becomes RGB 213 128 140, still "darker"?
The green and blue component are "close" (125 vs 119 and 140 vs 143) but the red is out of line (213 vs 243).
I think I'm slowly getting the gist of this tool...
Here's a fresh screen capture to illustrate:
This would have to be confirmed by an Adobe InDesign engineer but I am forced to conclude that the little Color Theme Tool floating palette is not color-managed? Meaning, it's colors are being displayed in the Monitor space without first being converted to the Document RGB space. That's what I think is the culprit in all I have seen over the last couple of days.
How did I come to this conclusion? Using a "screen color picker" much like the Digital Meter which comes bundled with the Mac, I noticed that the RGB values being displayed *inside" the Color Theme Tool palette were identical with the objects to which I applied the tool's colors. In the above example, if you hover over, say, the center swatch in the tool, InDesign display a ToolTip with the RGB values on that swatch. In this case, the "aqua" patch in the palette is shown as R=168 G=212 B=217. This happens to be the exact RGB recipe for the "aqua" object on the first row of squares (Colorful), center, exactly the same.
As I was mousing around the image with my slick "screen color picker", that's when I noticed the discrepancy. In actuality, what InDesign is sending to the screen to display that center aqua patch is not 168 212 217 but rather 181 209 219!
It became clear, to me, at that point, that I was not comparing apples with apples, meaning, my beautiful NEC 27" wide gamut monitor is not rendering 168 212 217 the same as my Document RGB = sRGB "168 212 217", the colors I was seeing all along in the Color Theme Tool palette (or panel, chose your UI preferred terminology) were much more saturated than anything InDesign could show given the choice of sRGB Document RGB color space.
I think that's the reason for the discrepancy I'm seeing.
If that's indeed the case, then the Adobe InDesign engineering team has its work cut out for the next version...
That hardly seems so, Rob.
I just did an experiment with the Color palette, to test how it is being color managed to the monitor profile :
Sadly, I wrote some of my comments in french.
It boils down to this, every UI elements is "normally" converted RelCol to the screen (monitor profile).
That's the same behavior as Photoshop and it's the only logical way to do this.
The problem with the Color Themes Tool palette is that, although the RGB values are correctly displayed and assigned, the appearance of the palette itself is NOT being managed.
Take the case of 100% Magenta above (Cyan and Yellow did not make much of a difference...).
When I select the "Convert to RGB" option in the Color Theme Tool option, given that the "Document RGB" = sRGB (in my case), a RelCol conversion should result in R=229 G=0 B=126. And this is the RGB value BEING displayed. That's correct.
What is NOT correct, though, is that this RGB value is dumped without any further color management to the video card!!!
Creating a visual discrepancy between the expected and the actual.
On a wide gamut monitor like mine, the difference is even greater.
I think I'm going to turn this into a bug request after all...
It is a genuine bug. The colors are not managed correctly to the screen.
I'll let you know what the engineering team response is, if any.
More likely a limitation of a web based panel. There's nothing subtle about this so it won't be news to anyone at Adobe. Without a connection I even get 401 page not found errors inside of my app panel, here it is from Photoshop.
I did not stumble on 401 yet...
Isn't it interesting, what goes on behind Photoshop's and InDesign's Adobe Color Themes panel.
Here are some further observations.
First, a comparative screen capture :
The relative appearances of the palette is the same, except for the gray background which is lighter in Photoshop. (Could be my "Interface preference"?)
It is logical to expect that the RGB, Lab and CMYK numbers respond to the ICC profiles assigned to the document but they only the CMYK numbers do change with changes in Assigned profiles? For some reason, the RGB numbers are forever stock on sRGB? And that's true of both Photoshop and InDesign.
Another "feature".
but they only the CMYK numbers do change with changes in Assigned profiles?
The response is only temporary—as soon as you save a theme everything falls apart because of the link to the web app.
So again it doesn't take any elaborate testing to see there's no CM with saved themes. Build a theme with CMYK primaries, save it, and reload.
Above theme saved. 100% cyan would never convert to 0|255|255
0/161/227 is bang on Coated GRACoL to sRGB, Rel Col with BPC.
Right but the point is those values don't get saved unchanged. I can save them CM'd to the Swatches panel but not to the Theme panel.
only in Adobe's twisted color profiles world, Rob
No, it would never happen with Adobe's CM—at least if the CMYK profile was captured from a press sheet. I'm using the example to show that the online app isn't using the Adobe CM system because of the interaction with a web browser.
Some browser's will honor embedded profiles, but there's not the comprehensive CM system in place needed to make conversions in a web app. So it's either not possible or too expensive to code. If you view a CMYK image in Firefox or Chrome you get the same effect. PS vs. Firefox:
On Windows 10, Edge does not have any color management capabilities 
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