I was sent this pic by a client who wondered if the green skin of this Meyer lemon meant that it had Huanglongbing disease, a malady that is threatening Southern California's citrus groves. He also added that other than the green skin, the lemon tasted the same.
Well this citrus probably does not have Huanglongbing. The greening associated with the disease is usually very uneven. What is happening is probably a process called 're-greening' that is common in some oranges, like Valencias. After the oranges ripen their skins start turning green again. This does not change the sweetness of the orange or its taste. This 're-greening' can happen to Meyer lemons, because they are actually oranges that taste and look like lemons. Also, 're-greening' occurs more frequently during warm winters, which we are currently experiencing.