We are going to get technical for just a bit. Color for concrete is actually not a dye, stain or paint. Though these terms are usually used to explain to customers, the color is actually pigment. Pigments are mined from the earth, or most often than not manufactured in big chemical plants. They are available in granular forms, powder, and liquid. Just a heads up, none of these forms are better than the others.
To understand the coloring process you need only know that pigment particles are ten times smaller than particles of cement. When color is added to any cement based mix, the small pigment particles cover the cement particle. This means that the amount of color to add is based on your cement sack mix, so you have to account for each sack mix individually.
Two Key Factors
The most critical factor that affects color is the water to cement ratio. Having control over the water added to the concrete mix is essential to producing a consistent color. The addition of water will change the color of the concrete, typically making it lighter..
The second key factor is the role of the gray cement. The color you add to the mix will have to overpower the gray in the concrete. The color of the concrete and the color of the pigment will create the final color we see. This explains why colors made from gray cement are darker earth tones. If you spend a little extra for white cement, you can achieve brighter color concrete.