The green color is from chlorella having more chlorophyll than anything else. It is a green algae. Spirulina is a blue-green algae. It has much more chlorophyll than any land plant. Chlorella has more but does not have have the beneficial blue pigment that spirulina has. So which is better?
No need to compete. Which tastes better-- a toasted bagel with nothing on it or cream cheese by itself? Together they taste much better. You can buy one of the many green drinks out there. They have spirulina, chlorella, barley grass and wheat grass. Note-- there are many experts who argue that one of the above superfoods is the very best and most nutrient dense. See this page (greens drinks) for more information on a few of the greens drinks. They even put them in food bars.