Atmospheric gas changes, and their effects life
The Earth is blue (at least the non-land mass) because of the light our atmosphere refracts from the sun. A planets color is primarily determined by distance from sun, not from gas components. 

Most gas does not refract light. Therefore a planet's gaseous composition can not be identified based on color. 

To elaborate on your primary question, gas composition balance is essential to most life on Earth. Carbon dioxide, for instance, is responsible for photosynthesis occurring in plants. Different concentrations will affects photosynthetic rates. Another example is that CO2 levels, CO levels, and hexa-fluoro-carbons affect the amount of heat trapped in this planet. 

Gas composition is highly delicate and must stay in balance to preserve life on Earth.