A background color can be any color. You can go with the basics, black, white, grey, tan, cream. Or you can match the room it may be in, blue, yellow, green. You can go super modern with orange. You could continue with the Farm Girl Vintage look and change the background OR keep the background and use wild/intense colors in the blocks. As always, your quilt, your rules. I always consider patterns as a guide line, not a must.