I spent 26 years studying concrete with everything from the naked eye to a 1200X petrographic microscope. It's color is…
Depends on the era, the area where it was made, and the color of the sand that went into it.
Most concrete prior to the 1960's was very pale light gray or very pale light tan when placed, but weathered to a grayish buff to nearly brown, depending on the amount of iron in the raw material used to make the portland cement that is its binding component, and the kiln temperature at which the raw materials were clinkered.
Prior to 1960s, a good color to represent concrete can be made by mixing light tan with a light gray. Then apply very light, separate washes of each color in an irregular pattern. The older the concrete is, the darker and browner it should be unless exposed to tropical or desert sun, in which case it gets tan but stays light. Some concretes from this era are distinctly pink. Low grade concretes from this time period will be nearly white.
Occasionally concrete in the early 1900s was very dark gray.
After 1960, concretes generally became grayer, weathering to warm white. Modern concretes, especially those that are "high tech" are generally darker gray, and stay gray as they weather. However, concrete can be made to almost any color.
Concrete that has been exposed to fire below the concrete dehydration temperature often turn pink near the surface.
Concretes made with certain mineral admixtures begin as a medium deep gray green that rapidly weathers to pale medium tan. These concretes were popular in runways during the 1970s and 1980s.
So the answer to your question is: any light, pale shade of gray, tan, or a mixture of both. Only an expert could tell if your color was too far off to be real, and there are very few of us. If it looks like concrete to you, it probably looks right to 99.9999999999% of the population.