N SCALE CONCRETE BLOCK

I plan to build an extension onto a building that’s made of concrete block. I’m in N scale, but plan on using some HO scale brick sheeting, as I’ve heard that HO brick can be used for concrete block in N.

My question is, what shade of gray should I paint it?[?]

I feel if the extension is to look ‘original’, paint to match the main building; if it is to look ‘newer’, than any shade would be OK.