When you make a project with scrap yarn, there is no way around the fact that you are going to have to deal with yarn tails. Lots of yarn tails.
It's what happens when you are working with at most a few yards of yarn at a time. Having an efficient way of dealing with these yarn tails is half the battle to accomplishing a successful scrap project.
Dealing with all those tails is why this is a crochet project in the first place, and not a knit project. Burying tails is a lot easier with crochet and both sides of the finished project can look neat and tidy. At the same time you don't want to have to deal with all those yarn tails at the end of the project, because weaving them in can be tedious. I tend to work on them in bunches. Here's how I do it.
First of all, I am not a purist about not tying knots in my yarn. Some folks act like you have violated the Eleventh Commandment if you tie your yarns together. I might do it differently if this were heirloom lace, but for a utility blanket, I'm not worried about knots. They let me attach a new piece of yarn quickly and keep on crocheting. The one thing I did decide with this blanket was that I wanted the knots to come at the edge of a space, not in the middle of a 3 dc cluster. This means I have some tails that are a bit long, but I go as far as I can, then tie on a new ball and go for it. When I tie on a new ball I try to leave myself a tail of between 4-6 inches in the new yarn. It makes life easier down the road. You're going to want more yarn than you think you do. You can make do with less, but it just makes the last step harder.
When I get back around to where I made the join on the next round I then start working those tails into the fabric so they won't come out and dangle with washing and use. I've learned over time that just trying to slide them under the 3 dc clusters isn't enough; they do work loose. So I start by working the tails through the tops of the stitches, matching colors.
Then I can go ahead and crochet over those tails, reinforcing the idea that they are supposed to stay neat and tidy.
The final step is to thread that yarn into a needle and work it under a 3 dc cluster in the opposite direction from the back side. I skip one strand of yarn when I do this, so it won't just pull through and undo what I am trying to accomplish. If you look for it, it shows, but not enough to be really noticeable. I've learned that this doubling back makes the yarn tail a lot less likely to work itself loose and cause a problem later on. I often do this last step in batches rather than sewing in each one as I go along.
So this is what the blanket looks like at the end of Day 4. I've used up between 5 and 6 oz of the black yarn and probably about 30 balls of scraps. I have no rules about how I change colors other than to try not to put two balls that are really close in color together, but even that's flexible.
I still have to show you how to end it off. When I get there, I'll write a post.