Nomenclature
These cells are so-named because they can be visualized by staining with chromium salts. Chromium salts oxidize and polymerize catecholamines to form a brown color, most strongly in the cells secreting noradrenaline.
(The enterochromaffin cells are so named because of their histological similarity to chromaffin cells (they also stain yellow when treated with chromium salts), but their function is quite different.)
Read more about this topic: Medullary Chromaffin Cell