Customers will often request a red leaved tillandsia and are uncertain when I offer them a green one with the promise that it will change.
The red or purple colour present in the leaves of many Tillandsias is caused by a pigment called anthocyanin. Anthocyanins play an important role in plant processes. Firstly, in pollination; anthocyanin pigments absorb UV light strongly, which attracts insects using wavelengths that are not seen by the human eye.
In the above images the green plants are the same species as the red ones next to them but have not yet come into flower, the red plants have flushed a deep red to help attract pollinators and this red colour will fade after flowering.
The second important role that anthocyanins play is to protect the plants DNA from sun damage. Anthocyanin production can be induced by high light levels, particularly blue and UV light; temperature; water stress and carbohydrates. For Tillandsias in particular, when grown in strong light, anthocyanin production increases and causes leaf colour to change.
These images clearly illustrate this.
In each picture the plant on the left was grown outside in bright light and the one on the right was grown under 20% shade cloth. The effect of growing in bright light is very clear.
When grown in bright light, particularly if there is little humidity then the water needs of the plant need to be increased. However, we have found that when grown in the open plants are more able to take advantage of rain and dew and so often have their water needs met.