About three years ago ago, I knitted a multi-coloured cardigan to use up some of my stash, and I decided to try using the magic knot to avoid having to sew in hundreds of ends. It was one of the best decision I ever made. The cardigan has been through the washing machine many times since then, and to my amazement, the knots have all held so far.
I think that the link above will take you to a You Tube tutorial that explains the magic knot and shows how to tie it.
It took me quite a bit of practice before I was confident enough to rely on it, and it might not be suitable for every project, but certainly for my cardigan it worked well, Even though it took time to tie a knot for each colour change, , it still felt a lot less tiresome than having to sew in all those threads at the end.
Double borders are the answer when you have frequent colour changes, to save having to sew or weave in ends - and essential for mosaic crochet where you change colur each row..
Bear in mind that mosaic crochet is double thickness so a thick border works very well. You might not like the look on a single thickness blanket so do a test piece first.
You may also have to make some adjustments in the slip slitch foundation row if you have stitches of different heights at the edge. Mosaic usually has a single border stitch to work into.
Video tutorial from mosaic expert Tinna Thorudottir Thorvaldar here: