The second and third last picture show the same dialog, just that the second last one has the Define Custom Colors section expanded.
You are correct, however if in the RTF editor you select the context menu, then Font, you get the following results for
Text colour ... opens unexpanded dialogue
Background colour ... opens unexpanded dialogue
Underline colour ... opens expanded dialogue <--- why?
If you open Paragraph, you get the result for
Background colour ... opens expanded colour dialogue <--- why?
If you open Table, you get the results for
Cell border colour ... opens expanded dialogue <--- why?
Cell colour ... opens expanded dialogue <--- why?
In the last picture, clicking the select button would take you to that same dialog (RGB fields were provided at that dialog level to save you one more level of dialog).
This is true, but I would question the actual utility of this, versus the confusion of a different dialogue, and ''having'' to know that the select button takes you to the colour dialogue.
The 4th last dialog is the standard Windows font chooser dialog (provided by common controls). Please note that the color dialog (the other 3 dialog instances) is also a standard Windows dialog. So if there is an inconsistency then it is across Windows as a whole. I do not have a say in the usage of these dialogs, but if it were up to me, I'd certainly prefer to use the standard Windows dialogs ahead of custom ones as that is what the wider user base is familiar with.
You may be right about the windows dialogue, but when I use word all the dialogues appear the same, no matter what item I am formatting.

The other two (context menu/combo box related color choosers) I'd have to have a little bit more of a look into - so your issue report will lend weight to that.
Thanks
IMHO a consistent user interface is preferable, and in the case where dialogues are on a diagram and perhaps can be justified as being different they should at least show the same default colours, and provide the option to proceed to the standard dialogue box.