Lemon and lime trees in pots

Question

Someone gave me two planters with citrus trees growing in them. Against all odds, they bloomed and have set fruit! One was supposed to be a lemon, the other a lime, but the fruit on both is green. Living in the north country, I have never seen citrus trees growing, but I expected immature lemons to be green. So one question I have is — are immature lemons green or yellow? The second question is how do I know when the fruit is ready to pick?

Answer 1

Immature Lemons are green.
These articles have more information.

https://www.gardeningknowhow.com/edible/fruits/lemons/how-to-grow-a-lemon-tree.htm
https://www.gardeningknowhow.com/edible/fruits/lime/lime-tree-tips-care-of-lime-trees.htm

Answer 2

Thank you — the fruit on both trees is green, which makes me think that one of them is a lemon tree (with immature fruit) and the other a lime tree that may be ready to pick. How do I know when the fruit is ready?