I agree with those who suggested maybe just matching each section you're quilting. Unlike machine quilting, you only grab 12-18" of thread at a time for hand quilting anyways so it's easy to change thread color. The only thing you'll want to consider is what it will look like on the back since it's the same thread front and back.
Personally, I think it also might be fun to do a couple of trees in a green thread (same tone as the evergreen). Or you could do the whole thing quilted in a red or black. So many beautiful choices that will really highlight your beautiful piecing. I can't wait to see the results!