A concrete color?

Why not look around the concrete structures around you to get an idea of what colors to base your project on. Concrete can take on shades from dark dirty white to lighter grays. Depends on the materials used to make the concrete and the amount of weathering...if they were placed in low damp areas, moss and lichen would have probably grown on them.

Concrete of that era was often brownish, ranging from a fairly deep tan to a nearly pinkish tan. The color of concrete is primarily determined by the color of the portland cement used to make it (refering to concrete as cement is incorrect) and the color of the fine aggregate (sand) used to make it.

Older cements often had a high iron content, and were often not as uniformly sintered as modern cements, which are more closely controlled. This generally resulted in overburning to some degree, resulting in the browner cast. Most modern concrete (post 1960s) tends to be grayer.

Concrete generally becomes paler and lighter in color with age due to atmospheric carbonation of the surface. Formed surfaces (those against which the concrete was cast) will lighten more quickly with the passage of time. Finished surfaces (trowelled or broomed) will be darker, and will stay darker longer.

Concrete made before the 1960s, and some made in the 1960's, generally has a high water to cement ratio, generally 0.5 or higher. For the 1940s and 1950s, 0.65 was common. This concrete is very porous, and carbonated rapidly. It also trapped fine particulates, quickly acquiring a darker surface wherever it was exposed to debris, and providing excellent habitat for biological growth under the right conditions.

By comparison, high quality concrete for general purpose use these days will have a water to cement ratio of 0.45 or lower. High strength, modern concretes (such as in a modern runway) might have water to cement ratios approaching 0.25. The use of slag cements imparts a green color to new concrete, but this changes to light tan with exposure.

Hope this helps. 

Excellent information, I've used a combination of grey, a little white and a little reddish brown coloured acrylic sealer (paint) to match concrete from older eras when doing concrete repair!  Modern concretes tend to be a whiter grey from carbonation, finer grinding and less of a reducing condition in the kiln when the cement clinker is manufactured.  Colour is often measured against a standard colour board used in photography ie 90% grey down to current cements that run 30 - 40% grey.