The expression pigment does not necessarily indicate the same substance. For example, although powdered iron oxide red pigments may have the same appearance, one may be many times stronger than the other.
When using pigments for coloring concrete, pigment tinting strength (color strength) is the most important property in selection. Tinting strength is not only affected by purity of the pigment, but also by grain size. A red pigment that appears very dark in powder form does not necessarily have strong tinting strength.

Two types of iron oxide pigments were used (with very large difference in color strength) and the relationship between the amount of pigment used and color strength of the colored concrete were plotted to give a typical curve that extends to a saturation point as shown in the graph above. For pigment 1 which has strong color strength, the amount of pigment added was 5 -6% of the cement amount, and the saturation point is almost reached, but this was not the case for Pigment 2 which has a weak color strength. In addition if, 10-12% or more is not added, the same color cannot be obtained. If the amount of pigment that must be added in order to obtain the same color can be determined, then relative color strength can be determined. Adding 3% of pigment 1 gives the same color as adding 6% of color 2, and 5% of pigment 1 must be added for 10% of pigment 2. This is also clear from comparing the pictures below. Thus the cheaper pigment is not necessarily the most economical.