Updated July 20, 2021.
You know the feeling, you are going to run out of thread before the project is finished.
You’ve already starting stitching, so you can’t use my stripes method (explained in the link).
What do you do when you’re using a stranded thread?
First off, stop stitching this color immediately. You want to save as much of the thread of your first dyelot as you can.
Second, buy the thread you need and one skein more than you think you need. Get the same dyelot if possible.
If the dyelots are not the same, then you will use needleblending to move from one dyelot to the other. The process is the same as shading: you will replace one strand at a time until you are only using the new dyelot.
But how do you decide how many rows to do for each blend? Assume that, at most, one half of the remaining area should be used for the transition, although it can be much less. But remember, the wider the transition are is, the more seamless it will be.