According to Plant Kingdom Class 11 notes,

The presence or lack of pigments is the primary foundation for classifying algae. The categorization is as follows:

Chlorophyceae: Green algae are members of the Chlorophyceae family. Because chlorophyll a and b pigments predominate, they are usually grass green.

Phaeophyceae: Brown algae, also known as Phaeophyceae, are mostly found in marine environments. Chlorophyll a, c, carotenoids, and xanthophylls are all present in them. Depending on how much of the xanthophyll pigment fucoxanthin is present in them, they range in colour from olive green to various shades of brown.

Rhodophyceae: Rhodophyceae members are usually referred to as red algae due to the preponderance of the red pigment r-phycoerythrin in their bodies.