Nope .... never any hard and fast rules in quilting!
Your quilt ... do whatever YOU want to do!!!!!!!!
Some do samplers where every block is different.
Some use one background fabric and switch up the others.
Some use all the same fabrics in each and every block.
Some choose fabrics that are very colour and style coordinated.
Some go totally scrappy and throw caution totally to the wind!
(and yup, I've done them ALL!
)
(wait ... nope, I haven't done the fully matchy-match fabric one!)
Whatever you want to do ... you can do!!!!!!!!!!