Why are algae and ferns both green

They both are plants. All plants have chloroplasts, which are tiny little organelles within each cell that capture the light of the sun and turn it into energy for the plant to use. Chloroplasts do this by using their green pigment, making the leaves of plants to appear green.

Algae and Ferns both have green pigment chloroplast inside an organelle call the Chloroplast which allows them to carry out Photosynthesis and that gives them the color green