Final answer:
Green algae have a green color due to the presence of chlorophyll a and b in their chloroplasts, similar to plants.
Step-by-step explanation:
Green algae are closely related to plants, and chlorophyll is what gives them their green color. The pigments responsible for this coloration are chlorophyll a and chlorophyll b, which are both found in the thylakoid membranes of chloroplasts in plants and algae. These chlorophyll molecules are nearly identical except for a small difference highlighted in a red box in some diagrams. Chlorophyll a and b absorb light primarily in the blue and red wavelengths, but not in green, which is why this light is reflected and why the algae appear green to us. It is important to note that other pigments like β-carotene contribute to coloration in some organisms, such as the orange color in carrots, but they are not responsible for the green color in green algae.