You are what you eat.  At least that is what has been hammered in our brains since the food pyramid became popular.  But the good news is that the healthy foods your body takes in, eventually come out.  But not in a way you may think.

proteins in ejaculate

Both male and female ejaculate contains carbs, amino acids, and proteins.  When the ejaculate fluid dries, it will dry yellowish depending on the amount of protein in the secretion.  The higher the protein found in the secretions of the ejaculate, the more yellow it will dry