The most important rule to follow is to be consistent. Choose materials, develop and test mix methods, establish site and placement conditions, and then avoid changes. Of course, the color must be of reproducible high quality. Ask about quality assurance . Changes in cement or aggregate can affect the appearance of colored concrete.
Gray cement works well for most colored concrete.
Gray cement works well for most colored applications. White cement may be necessary to achieve maximum color clarity or delicate shades. Other cements may be used to achieve special effects. Similarly, the concrete aggregates should be selected with consideration of their effect on color. The fine aggregate can have an especially significant effect.