I would quilt either all the charcoal, or all the blue. The quilting on the back will then echo the block pattern. If each block is 12", you will definitely need more quilting.
I would use a couple different patterns for the outer squares (I get bored easily, and changing makes it more fun).
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If you need to quilt both colours, I would do a straight-line pattern in one colour, and a curvy/swirly pattern in the other.
Your quilt is lovely - good luck with the quilting!