I've been saving up green plastic bottles for a few weeks now with the vague intention of recycling them to make a cold frame or greenhouse. Are green bottles ok to do this with, or would they need to be clear plastic bottles?
A clear film will transmit the most amount of light. Blue and green coloured plastics will transmit a lot of the light in the blue to blue-green wavelengths, but cut out much of the light in the red wavelengths. From the diagram above looking at PAR, it can be seen that red light is the most efficient waveband for plant growth. A blue plastic is likely to produce a slower growing, shorter, tougher plant.
Also of interest is that plants have been shown to use far-red light as a way of determining how much competition there is for light. This is because green surfaces, such as leaves from other plants, reflect a lot of far-red light. If the plant perceives that there is a lot of competition, it will put less energy into growing roots and more into growing tall, quickly.
A green plastic is likely to produce a stretched, slow growing, poor performing plant.