MSU Extension mentions a few causes of purplish coloration on corn foliage, but that are referring to outdoor-grown corn, and the symptoms pictured are not exactly what your photos are showing. In either case, it does not look concerning, and might be a response to light level depending on the intensity of light source that you are using. Has the plant been fertilized with a fertilizer that includes all of the basic nutrients? (N-P-K plus micronutrients like manganese, magnesium, iron, calcium, sulfur, etc.)

Corn is not an indoor-grown crop, and we do not have diagnostic information available pertaining to unique problems that might arise for indoor-grown plants. Washington State University Extension has a publication online about growing baby corn, if useful, though it is geared towards farm settings. Cornell University's sweet corn growing information includes a couple mentions of baby corn as well as nutrient deficiency indicators for the crop as a whole.

Miri