What is causing the initial discoloration of the chicken?

Meat and meat products have very short shelf life. These are easily spoiled by microbial contamination. Any discoloration in meat and meat products is a sign of bacterial contamination. Thus, it is very important to inspect the uncooked meat before cooking it.
The discoloration of chicken to shades of gray or dark color or yellowish color indicates food spoilage.

The initial coloration of chicken is caused by the growth of Pseudomonas.