As a rule they are highly coloured, the colouring matter being contained in the cell-sap, as in blue or red flowers, or in plastids (chromoplasts), as generally in yellow flowers, or in both forms, as in many orange-coloured or reddish flowers.
Cream-coloured flowers are regarded as white because cream is due to yellow plastids and not to sap colour.
Chromatophores.The chromatophores or plastids are protoplasmic structures, denser than the cytoplasm, and easily distinguishable from it by their color or greater refractive power.
The coloring matters are not dissolved in the stroma of the chrornoplast, but exist as amorphous granules, with or without the presence of a protein crystal, or in the form of fine crystalline needles, frequently curved and sometimes present in large numbers, which are grouped together in various ways in bundles and give the plastids their fusiform or triangular crystalline shape.
In addition to the plastids, there are found in some plant-cells, e.g.