The Blyxa in the photo I showed in my previous post was in the tank for over a year.
Here is that same specimen (in the middle of the photo) 3 months earlier with identical dosing levels:
There are a combination of factors that affect the pigmentation changes in plants. Additionally, the factors are not always the same for different species. In general, the purpose of pigments has to do with the ability to harvest the energy of various wavelengths of light or to reflect and protect the plant from excessive energy of certain wavelengths. Chlorophyl is a green pigment which uses Nitrogen in it's molecular structure. Other pigments, such as Carotene are orange/red and do not contain Nitrogen, therefore in some cases, under a Nitrogen shortage, there is a lack of Chlorophyl in relation to Carotene or other non-Nitrogen pigments which can cause the appearance of the plant to be more red since these pigments overshadow the green Chlorophyl. Thus was born the concept that a plant should be starved of Nitrogen in order to have the non-green pigments dominate.
While this is a plausible scenario, it is not the only one in which non-green pigments can dominate. Since the plant can respond to spectral changes, it can manufacture sufficient non-green pigments that can overshadow the green Chlorophyl. In this way it can take advantage of wavelengths of light that Chlorophyl is not optimized for.
The healthier a plant is the more able it is to respond to environmental changes, such as pigment production to account for spectral changes. It is not always necessary therefore to use N starvation to achieve the pigment alterations as many suppose. It's a much more complicated issue than simply having low nitrates, which can actually do more damage and will cause the leaf to go yellow, not red, if you fall below the Nitrogen threshold for good health. Likewise, just because a plat goes red it is not automatically a valid assumption that this is due to low Nitrogen levels.
Here is another example of pigment change under high (60ppm) Nitrate levels. This is Pogostemon Stelletta which has turned purple on one stem and yellow on another. This is on the same plant. Therefore, it's not a matter of "growing out" of a pigment pattern. It can happen at any time based on the environmental conditions and plant health. A pigment change MAY accompany a decline in health or a decline in some nutrient, but can just as easily accompany an increase in health and an increase in nutrient/CO2 level. It depends on the particular mechanism at play.
Cheers,