I'm not following you. When you start a new yarn at the beginning of the row, just leave 6" or so to weave in the tail and just start knitting with it. That's all you need to measure. Unless you mean something else...
eta, and yeah, i just start a new end when I run out of the old one. And I use knots, and mostly knit in the round or seamlessly. But I don't do color changes either.
sue- knitting heretic