White color is due to absence of carbonaceous matter. 0.6mm Microfossils are forams and fragments. Irregularly-shaped patches of coarse sparite are cavity fillings in micrite. Black color is probably due to micron-sized carbonaceous matter or clay. Notice the sparry overgrowth on rounded core with dusty margin ,that maintains optical continuity with crystal making up the plate.
Areas occupied by clean calcite represent initial porosity in bioclastic sediment.
The irregular - sinusoidal red band is a styolite , that represents a surface within rock along which extensive dissolution has taken place. The red color is concentrated clay or hematite residue left after removal of calcite. You can see three-dimensional shape of styolite on cut surfaces of hand sample 378. Notice that the calcite cement grains nucleate on the surfaces of the shell fragments. Some detrital angular quartz grains.