What's special about the bottom buttonhole?

Something’s been bugging me for a while now:
Why are the bottommost buttonholes on men’s shirts often sewed up with a different coloured thread? On about 2/3 of my shirts, all the buttonholes are stitched with thread the same colour as the shirt, while the bottom one uses a sharply contrasting thread. I can’t think of any practical reason that this should be so, and it stands to reason that it involves a certain amount of extra labour.

Can someone clue me in?

Maybe the buttonholes are sewn by machine before the fabric is cut.

That way the worker would know to just cut the fabric after the off-colored hole. No counting holes involved, less room for error, less wasted fabric.

I assume the make it the LAST hole because they figure you’re always going to tuck it in, so no one will see it.

Ok, I pulled out the men’s dress shirt that I have in my closet, because I had never noticed this. It doesn’t have a different color buttonhole on it.
But, this is the explanation I got when I asked about it at work.

When shirts are made in factories, they go through an assembly line process, with many different operators doing small parts of the shirt. The buttonhole portion of many men’s shirts is cut as a separate piece, because many times fusing is put inside, to help this part hold it’s shape.

Because this is actually a separate piece, the operator who sews it onto the shirt doesn’t need to waste time hunting for the top and bottom-these people are paid piecework, and it’s to their benefit (and the factory’s) to work as quickly as possible. The different colored buttonhole allows them to very quickly know which end goes which way-which is why off-white thread in place of white wouldn’t work nearly so well.

The bottom whole is used because that portion is normally tucked into the man’s pants, so no one sees the different color thread. It’s just a way to make the process go faster.

hole, hole, hole!!!
Ok, I’m better now, thanks.

That would be the replacement buttonhole, corresponding to the extra buttons sewn on the bottom of many shirts. That way, you always have the right number of buttons and buttonholes, even if you lose one or the other.

Hah – Reminds me of Elwood P. Dowd’s classic line from Harvey – “Please accept this flower, I seem to have misplaced my buttonhole.”

Thank you Sue & Laura for your (in retrospect, obvious) answers. None of my tailored shirts have weird bottom buttonholes, which seems to confirm everything. At last, I can get some sleep.