The sky will tell you the color of the air....the envelope of light. Look and think. Local color can call you like the sirens on the rocks, but remember that there is so much effecting the actual envelope. The local color- in this case green- is hardly present in its strong form. In the case of this painting there was so much humidity, (humidity, pollution and dust particles are a painters best friends) that the color was dense. The colors "bounce" of the moisture.