i worked in good supply for awhile. the tuna at delis and bagel places is tongul, not tuna, they are very similar and swim together. No one really knows the difference in the deli, but it's darker than solid white albacore.
while i'm at it, McDonalds chicken mcnuggrsts is not whit mat. if you listen closely, the will call it "LightMeat" Light meat is dark meat, the lesser valued, pierced with tiny needles of peroxide to bleach it white. People at McD's don't know that it's been processed that way, so it's no use calling thm. You can however call the purchasing agents. but no one rally cares.