What is the best way to tackle this?
 

My current quilt top (sorry, I'm using DH's laptop so don't have access to photos) has a middle section of predominantly cream blocks in a " + " pattern surrounded by dark brown blocks. I'm using the same dark brown fabric for the backing.

I am quilting a spiral out from the centre of the quilt using a light thread in both the needle and the bobbin, as it blends nicely with the cream feature blocks and makes a nice contrast on the dark brown back. My plan is to swap the needle thread from the light thread to a dark brown thread once I have spiraled out of the cream blocks so that the brown thread blends and is almost invisible with the dark brown background.

So, if I were to use dark brown thread in my bobbin can I switch my needle threads back and forth from cream to brown and vice versa at the edge of each different coloured section or should I quilt all the cream sections of the spiral first, secure them off and then swap to the dark brown thread and fill in the rest of the spiral whilst leaving the same brown thread in the bobbin?

Either way, is there any particular way I should be securing all my ends?

Are you using your regular sewing machine or a long arm?
You can switch color threads as you want to, or you can do all one color then go back to do the next- that’s a choice you can make.
Securing ends different people do it different ways. A popular method is to pull the bobbin thread to the top, leave ends a couple inches long then when done quilting you tie them in a knot, thread them onto a needle and pull the knot into the quilt sandwich. Cut them off at the surface. Another method is at the start and stop take a few very small in place or close to in place (3-4 stitches over each other) then clip them off. ( this method is used often with long arm quilting)