They look good for granite etc, but maybe need to be a slightly more "yellowish-grey" for concrete, as you mentioned. Most of the constituents of concrete are sand and aggregate [gravel] which tend to give it a warmer tone. I'm thinking concrete used for buildings where natural gravel is used, not roads which use crushed rock aggregate that is almost invariably light grey and has a cooler tone.
Wet concrete [ie cured concrete that has been rained upon] looks a lot darker than dry, which, as was mentioned earlier, should be a pale grey.
Of course, someone will mention the colour of the Atlantic Wall in France, which will completely contradict my whole post :

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