Color change no knot is useful for both adding a new skein to a large project, and changing a color at an exact location. It also solves those dangly ends on the sides of, or in the middle of your work, and solves the need to weave ends in when you are done with a project. Even though I've found some wonderful, quick ways to weave ends in, I still do not like doing it.
I've been using the color change no knot for decades now. About the only time the join isn't tight enough is with items that get a lot of abuse (such as a dishcloth), or with lacy items that are made of mostly chain stitches. It is my preferred method for all clothing as sometimes a knot can be felt in the fabric.
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No matter where you are in your project the old color should have a long tail end left. Make a loop (as pictured below in yellow) with your new color. DO NOT finish your stitch. In the picture below I am doing Single Crochet (this works with all stitches) so I have two threads left on my hook.
Place the loop over your hook, just like it would be the last loop you were going to pull through the stitch you're using. All ends should be on the back of your project.
Hold both ends (old yarn and new color) and finish the stitch with the new color.
Both loose ends should be brought up across your work (the reason is doesn't work with a chain stitch) and you are going to crochet - around - them. This process hides the ends as you are working, instead of having to go back and do it at the end.
Do a few stitches holding both ends (5 or 6 is ideal, no fewer than 3, more than 6 is over kill).
Drop one of the loose ends (usually the shortest), and continue a few more stitches crocheting around only one loose end.
By dropping your yarn at different locations you don't have a bunch of stuff happening by one stitch.
Give the ends a little tug to make sure they are snuggled inside the work nice and tight. Don't pull them so tight that they warp the original stitch or change the shape of the row. Snip the ends off. Then just give the area a little wiggle and the ends should fall into the stitches to be lost.
In the pictures below you are looking at the back where I snipped the ends. and at the front. The color change can hardly be seen on either side.
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