Lemon or Lime?

A couple of questions...how do you tell if a lime is ripe?  No, this is not some goofy, little joke. I am serious! Just how do you know when a lime is ready to be plucked from the tree?  Lemons, grapefruit, oranges, Satsumas and kumquats are easy!  They change colors.  All summer long, these fruits will stay a deep green but come late fall, they suddenly exchange that for their bright colors proclaiming their readiness to be eaten.  But that lime...that lime that is green all summer and, well, stays green all fall and winter if you let it!  Just what is the magic sign that lets you know when it is ripe?

Another question..when the fruit is still in the "green" stage, how can you tell a lemon from a lime?  I ask this because I have several of each trees.  All are holding a nice number of fruits but I have no clue which are which!  When we planted the trees, I could have told you but that was years ago and a lot has happened since then.  For one thing, the trees froze to the ground during one particularly hard winter.  I was ready to yank them from the ground and start again when Michael insisted that I "give them time."  I did..they regrew and now are loaded with green blobs.  Now, do I have lemons or limes...or both?  Or perhaps a limon!  Maybe they got all mixed up and are now confused themselves!  I humbly ask you to compare the two pictures.  Are these the same type fruit?  Or are they different?  Is one a lime and the other a lemon?  Both limes..both lemons?  The pictures are from fruit on different trees.

I was out back in the citrus trees and noticed that the limes (or perhaps lemons!) were getting quite large.  This got me to wondering about when to pick these things!  If, perchance, these are lemons, they will change to a lovely yellow but the limes sure had better stay green.  At least, I have a few more months before I have to worry about which are which!  November should be the time to start picking the citrus fruit if these are anything like the grapefruit.  So perhaps my pondering is pointless!