According to the NCERT Class 11 Biology Chapter 3 Plant Kingdom Notes,

The presence or lack of pigments is the primary foundation for classifying algae. The categorisation 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. 
• Rhodophyceae: Rhodophyceae members are usually referred to as red algae due to the preponderance of the red pigment r-phycoerythrin in their bodies.