I start with machine in needle down position, drawn the bobbin thread up, take 2 stitches in place, run the path to where I want to end, draw the bobbin thread up again and take 2 or 3 stitches in place. Cut the thread and start again in another place. When I am all done, I go back and using one of the sewing needles that have the easy to thread eye, I thread the needle and draw the thread into the batting for a couple of inches and trim.
As far a color, it all depends on if I want the stitches to be part of the design element.
If NOT, I use whatever color matches as closely as possible to both the top and back.
If Yes, I often use varigated thread on the back if it is a solid, I like the effect. There are so many great threads out there no, blendables, twisted, varigated, so I like to play with the effects. I make a small sandwiched sample and try out the different threads to see how they look and then decide.
It's all a matter of personal taste, there are no longer rules that apply as far as I am concerned. Years ago there was such a limited array of thread colors, most quilts were done with plain colored thread, white most often.
Aren't we lucky we have all the choices available today!