Hello. Just thought I'd share some information on this.
Plants all have the ability to exhibit red and green colouring. In most plants, the green is dominant as this is a reflection of the chloroplasts which are abundant in all plants (chloroplasts being the place chlorophyll is stored and the place where food is manufactured - present in ALL plants).
When red exhibits itself, it can occur for different reasons.
For one, a high-nitrogen environment will promote the production of chlorophyll and make plants darker green (and healthier overall). Nitrogen is one of three macronutrients and used the most by plants. With decreased nitrogen, the green becomes subdued and gives other colours a chance to show through.
Red colouring can also show in cooler temperatures or when water becomes less available - this is more notable in land plants. Less water means fewer nutrients are available to the plant because all nutrients are dissolved in water for the plant to take up.
The other reason plants exhibit more red colouring, and probably the most prevalent reason, is because of intense lighting. This usually shows itself in the upper parts of plants where the new tissue is developing and closest to the light source. Plants do this as a way to protect themselves from getting sunburned. New tissue is much more tender than older tissue and it is also not shaded by leaves and stems above.
Plants use the full spectrum of light: red, orange, yellow, green, blue and violet wavelengths (all of these meld together to appear as 'white light'). They use red mostly and when you purchase plant lights, they are usually tinted red or pink to provide more of these wavelengths to the plants. Violet is the next in demand and the rest are used in far smaller quantities.
In a high light environment, plants try to bounce back the excessive and potentially harmful light (that would literally sunburn the more sensitive green tissue and destroy chloroplasts), which is mostly red. When a certain wavelength is not used by the plant, it is bounced back into the environment and our eyes and we see it as colour. The wavelength that is used LEAST by all plants is GREEN, hence why most plants appear green to us.
I hope this helps answer your question!
Krystal.