Chicken juices contain a soupy mix of proteins including haemoglobin (which gives blood its red colour when mixed with oxygen), and some myoglobin (which gives red meat its red colour when mixed with oxygen). Up to about 140F, they are unchanged, but heat them to between 140F and 160F and they lose their ability to bind oxygen and so their colours change. So if your juices are running clear, you know the temperature is at least higher then 140F and probably closer to 160F if they are indeed clear.
The question of what is 'doneness' is an interesting one. For most foods, doneness is a question of taste. After years of eating my chicken at 'at least 140F', I really like that taste. We usually cook foods to improve their taste, texture, nutritional value; very few foods traditionally kill or harm us if they are not cooked (cassava, certain beans are notable exceptions). Heating to 165F is recommended not for taste but to kill organisms such as salmonella - a tricky blighter that lives inside the cells of some other creatures and so can't be washed or peeled off.
I'm pretty sure that I'm the first generation cook in my family to own an instant-read probe digital food thermometer, so why is this now necessary? Well I may also be the first generation where salmonella in store-bought chicken is considered a saleable product and something to be cooked out by heat, rather than designed out by good farming and food handling practice. The 165F statement from food safety bodies was brought in to deal with such issues.
In France, there are still plenty of people who like their chicken very pink. With my own grown chickens, I will cook them till a skewer pierced into the deepest part of the thigh (but not near the bone), shows clear juices and on deep-breasted old breeds that can leave a tinge of pink towards the bottom of a (deliciously juicy) breast. I'm personally comfortable with that particular risk/reward balance.
But store-bought chicken? From an unattributed source? At $1:15/lb? Pass me the probe, please.
At least in the case of marinades containing acids (such as vinegar or lemon juice) or certain enzymes, especially from papayas, kiwis, or most commonly (at least in the US), fresh pineapple juice, a certain amount of denaturing of the proteins will occur at the surface of the marinated meat. This will turn it opaque rather than translucent--chicken will look kind of white. This is perfectly normal, and safe.
Depending on the color of the marinade, and the particular cut being marinated, some of the marinade may also penetrate into the meat, changing its color as well.
These are normal effects, and assuming you have otherwise respected good practices (keeping the meat refrigerated during the marination, not holding the food uncooked longer than would be safe without the marinate, and not cross-contaminating and so on), the product should be safe to eat.
In the case of your meat marinated triple the planned time, the outcome will depend on the nature of the particular marinade. If there was active enzymatic action, it could be very mush to the point of unpleasantness. On the other hand, if the marinade was mostly for flavor, rather than highly acidic, it might just have a more intense flavor from the marinade.
Edit:
I should add for clarity, when safe
above means when properly cooked
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Best Answer
You're wrong in your observation to begin with. There are tons of things with meat and seafood:
(thanks to Catija for most of the examples)
That said it might be somewhat less common for a few reasons:
And of course, simpler dishes tend to be more common, so you'll see much more with one kind of meat. Sure, there are more seafood-only dishes than combinations, but there are also more poultry-only and meat-only dishes than combinations