I tend to like to do all one color then roll back and do the other color. Here is an example of a quilt I was doing that way. This post was while it was a WIP
Agave Garden Going over the top with quilting sneak peek
And here is the completed top:
Agave Garden, the big reveal
I don't know what set up you have so you could run into some issues. I know of a LAer who did this and after doing all the first color when she got to the bottom she didn't bother to reload the sandwich from the backer bar to the bar for the top. She ended up with an unholy mess of batting in her bobbin race. This happened to her twice, on two different quilts! Perhaps she didn't know about reloading the bottom portion of the quilt or she left way too much untrimmed batting on the bottom.
When I do this I always unpin the bottom of the backing (which is now sandwiched and quilted to the batting and top) and reload it to roller that is meant for the quilt top. This serves several purposes:
1. The quilt sandwich is now rolling in such a way that the batting is completely encased in the roll, this is especially critical as you start working your way back up to the top with quilting from the bottom of the quilt.
2. The top is protected because it is on the "inside roll" of the sandwich on the bar as opposed to leaving it on the backside roller, which would leave the top on the exposed outside of the roll.
3. The backing bar acts as kind of a tensioner, much like a dead bar
I would like to add, black thread on black fabric is incredibly difficult to see. Be ready for some eye strain. It really doesn't matter how good your lighting is unless you are fortunate enough to have side lighting. Then the shadows created from the side light gives you an idea of where you have already quilted. I also like to mention, I think variegated thread looks spectacular on black. Actually any colored thread looks good on black. You may want to reconsider doing black thread on the black.
Quite honestly, your piecing and all the colors of this quilt make such a bold visual impact I would consider not custom quilting and simply do a panto on it. If this were mine I would choose a very lightweight thread like Wonderfil's Invisifil, Superior Microquilter or silk (Superior Kimono is very nice but spendy) in a very subtle color like a moss green or soft gold so the thread sinks right in and all you really see is texture. Or I would use a monofiliment like Superior Monopoly or Filtec (Glide) Essense or YLI's invisible.