ACTH (Adrenocorticotrophic hormone) stimulates the adrenal glands to secrete its hormones.
hGH (Human growth hormone) also known as somatotrophic hormone is responsible for the growth of long bones, muscles and viscera.
TSH (Thyroid stimulating hormone) influences the structure of the thyroid and causes it to secrete thyroid hormone.
I believe it’s called perculation
scientists can test differences of the area with pigmentation by observing which is lighter and which is darker however they use microscope to look the difference of the pigmentation over the cells.