This picture is just one of my thread boxes. I had to fish out all kinds of stuff that had wandered in - ya know that spool of velcro, ribbon, and other knick knacks. Anyway, this is just a reminder to specify thread color on spec sheets.
Most of the time, manufacturers know to match the thread color to the body of your design. If you hand them a sample, then they will reproduce it down to the thread color. Most manufacturers are very good about this, so spec'ing the thread color is usually overlooked.
But every now and then, you will run across a rare manufacturer that is either color blind or will use whatever thread they have on the shelf. It may or may not match. If you spec'ed the thread color, then you can go back to the manufacturer with a chargeback. If you didn't, well then you might be stuck. (I have seen this happen!)
Another reason to spec out a thread color is to match a screenprint, embroidery, or coordinating piece. The thread color becomes an integral part of the design. Would you really want to leave the end color up to chance?
It's really simple. On your spec sheets state "Thread color: American & Efird [color name] [color number]. You may even want to go to the extreme of including a thread color swatch, just in case the manufacturer buys thread elsewhere. Wind off some thread onto your fingers and make a little, mini-hank of thread and tape it onto the page. You can buy thread swatch books from American & Efird (You'll have to talk to a sales rep about a swatch book). You can even get thread dyed to match!