The answer to this question can vary greatly depending on the region/location, climate & type of sand/aggregate used. Get a good photo or, better still, try to take your color cards to some concrete structure of similar age and try to match that color.
Also, the scale being modeled has a huge impact on the amount of surface texture needed to be visually correct. One of the biggest mistakes I’ve made in the past was using textures & materials that were too coarse for n-scale. It might look ok initially, but fails terribly when photographed.
