I am beginning to see some corn turning purple this week most likely due to the build up of anthocyans in the plants. This can be seen in some varieties much more easier than others and is typically a result of warmer weather followed by cooler and wetter weather. Here are a couple photos of what I have seen:
Another possibility would be a situation of Phosphorus deficiency. Here is what the Plant Analysis Handbook for Georgia says regarding Phosphorus deficiency in irrigated corn:
Deficiency due to low soil P and/or inadequate P fertilization. Cool-wet growing
conditions can induce P deficiency even when the soil test P level is medium or
high. Correction generally occurs as the soil temperature increases if there is
sufficient P available for normal growth. Corrective treatment is difficult to
apply and may not be effective.
To determine if the plant is in fact deficient in Phosphorus a tissue sample would need to be taken and analyzed. A sample was taken in the field where the pictures above were taken and came back as having sufficient amounts of phosphorus. We can then say that the corn was purple due to anthocyans and will improve once the weather warms up again.