Excellent info on tyrosine and melanin synthesis can be found here:
The thyroid takes in iodine, obtained through food, iodized salt, or supplements, and combines it with the amino acid tyrosine. The thyroid then converts the iodine/tyrosine into the hormones T3 and T4. The "3" and the "4" refer to the number of iodine molecules in each thyroid hormone molecule.
Tyrosine is also the immediate precursor to the thyroid hormone thyroxin and melanin, which is the pigment in the skin that allows for tanning.