THIS PAGE is one of several explaining techniques about how to use concrete in small-scale art projects.
Concrete can by coloured or dyed with a limited palette of several colors.
Because the portland cement is caustic, some pigments that work well in paint media are attacked by the causticity, resulting in colour break-down over time. To be certain, you must use pigments that have been proven to last when mixed with concrete. Green is less common and more expensive. Blue is even more expensive. Most colours seem to be derived from iron oxide or cobalt.