I think this is an interesting one...I avoided citrus most of the time for the first few years of trying to implement this diet because I was told it was usually picked underripe and hard to find ripe, and could cause teeth issues. Some of my teeth became translucent on the edges anyway (probably due to switching to non-fluoride toothpaste or continuing to eat crap along with fruit and my body being too acidic?). I was afraid to eat citrus after that because I thought it might make them worse, but for about the past 6 mos. or so I've really been craving oranges and grapefruit and eating a lot of them, and my teeth haven't gotten any worse. I've since learned that those are high in calcium, which really helps teeth and alkalinity (buffering the acidity in the blood). Yes, I'm sure ripeness is important, but I'm not sure we should fear acidic fruit like I did. Living in Seattle, I'm not sure if I've ever had perfectly ripe citrus, but I can definitely tell a difference--some are sour and some are sweet. If they're sour, I think they are underripe. If they're sweet, they should be fine, no? In fact, I got a bunch of different types yesterday and had a citrus sampler with my hubby. Some from FL, some from CA, some from TX... Some of the oranges were lighter in color and sour. Some were nice and sweet. Interestingly, the organic ones were sour. The CA navels, the murcott tangerines, and the honey tangerines were all very sweet. Experiment! See what your taste buds say. Hope to hear from others, too.
Hard to find ripe oranges in store, they are usually picked unripe to extend shelf life and minimize loss.
An orange is ripe when it comes off the tree by just pulling it gently, and it should come off the stem. So if the orange you buy still have a part of the stem attach to them, they haven't been picked ripe for sure. This works with most citrus. You can also tell when a navel orange is ripe to the skin. A ripe navel shows wrinkles on the skin, and starts to soften the skin while still on the tree. Tangerines and tangelos also soften on the skin and the skin is sort of detached from the flesh, like if there was an air gap between the skin and the flesh. Pomelo skin shrinks when ripe, and you can almost see the inner parts of the flesh from the outside for the red flesh ones (red ruby), and they should come off the stem by themselves.
Hope this can help