Letter to the editor of Concrete Decor Magazine.
Everyone knows you should use white cement to bring out brilliant colors in your concrete projects What isn’t so widely known is how to prevent white specks from appearing in some of those deeper colors. For example, you’re creating a dark blue countertop and you use white cement and white sand to bring out the blue. After you acid wash the surface, you notice white shiny specks. The crystals in the white sand are showing through and reflecting the light. To prevent these white specks in the solid colored surface, use black marble dust instead of white sand. The black marble dust will tone down the pigment somewhat, but it will also eliminate those white specks.
Concrete Chemicals of California