Word does allow you to apply transparency to shapes but not to table cells or paragraph shading.
As you noted in the other thread, the eyedropper is a useful tool. You already have that in Powerpoint so you don't need to screen capture and use the eyedropper in Paint if your colour source is Powerpoint. I note that this does remove the transparency in Powerpoint though so after you get the RGB value, you will want to undo the eyedropper's action.
With Visio, it looks like your current method is the best option.
UNLESS, you could use an eyedropper tool that worked on any part of the screen - see
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