Canned tuna in the United States is graded by colour, and the categories are tied to species. Albacore, Thunnus alalunga, has notably pale flesh and is the only tuna whose product may carry the designation white. Skipjack and most yellowfin fall under light, and darker-fleshed fish under lower grades.
The colour difference is real biology, not marketing. Tuna flesh colour reflects myoglobin content in the muscle, which relates to how the fish uses its swimming muscle and its oxygen demand. Albacore carries less of it than bluefin or bigeye, which are correspondingly darker.
One practical consequence follows. Albacore is larger and longer-lived than skipjack, and larger, longer-lived predatory fish accumulate more methylmercury, so albacore typically carries higher mercury levels than canned light tuna. Health advisories in several countries reflect that difference by recommending different consumption frequencies for white and light tuna. Separately, the trade name white tuna has been abused elsewhere in the market, where it has been applied to escolar, an unrelated fish that causes digestive problems in some people.