The histology is that of thyroid gland. And the pink material is colloid. The thyroid gland stores iodide primarily as thyroglobulin. The thyroid gland has a specialized active transport system that very efficiently traps iodide from circulating blood and can accumulate iodide against a large concentration gradient. Within the thyroid, the iodide rapidly undergoes organification by which it is oxidized and covalently linked to tyrosine residues in thyroglobulin. The iodinated tyrosine residues gradually become coupled to form thyroxine, the major secretion product of the thyroid.