No! The flesh of younger fish is pink, as are fish feeding on krill and shrimp. Fish feeding on squid are yellow or orange in flesh color. Another reason can be extra cook time. We only need to cook our fish once because the quality of the fish is perfect as is, from care and quality handling from the time the fish is caught until it is canned. Other tuna companies must cook theirs twice because the meat is poor quality (bruising from mishandling, etc.) which in turn makes their fish more "uniform" in color from can to can. This is also why they must add oil or water to their fish; while we pack the fish only in it's own natural juices.
Most often it is white, but like other fish, flesh color varies according to what it eats. Farmed salmon would be an unappetizing grey from their pellet diet so that's why chemical coloring agents are used to make them look like "real" salmon.