While they make look great read leaves will not inherently produce more oxygen. The color of the leaf is simply a result of the natural pigmentation in the plant and the amount of chlorophyll that the leaves contain. If you’re looking for cleaner air, try growing a snake plant, their wonderful oxygen producers. Producing more oxygen is more heavily influenced by the size of the leaf/plant and the amount of photosynthesis that the plant is undergoing. Plants with a good supply of nutrients, air, and light and larger/more leaves will produce more oxygen.