Deficient myelination in the internal capsule of the brain is associated with neurodevelopmental delays, particularly in high-risk infants such as those born small for gestational age (SGA). New methods are needed to further study this condition and assess how it relates to early life nourishment. MRI technology has been effective at measuring brain growth and composition but lacks myelin specificity and is low resolution. The development of new quantitative approaches that are rapid and precise may complement MRI results with insight into the pathology of deficient myelination and efficacy of nutritional interventions. Color Spatial Light Interference Microscopy (cSLIM) uses a brightfield objective and RGB camera to generate phase map images in conjunction with a regular brightfield image. Using paraffin embedded brain tissue sections, stained myelin was segmented from a brightfield image and, with a binary mask, those portions were quantitatively analyzed in the corresponding phase maps. This technique was therefore sensitive to subtle variations in myelin density. The results of this study indicate a positive correlation between an experimental diet, rich in critical nutrients such as iron, and dry mass levels of myelin in the internal capsules of both appropriate (AGA) and SGA piglets. In summary, neonatal dietary treatments affect the degree of myelination in certain regions of the brain, irrespective of gestational size, and may therefore impact cognitive health.