Business should be allowed to tell their customers in any way they deem effective. Micromanaging the font and background is absurd.
If we hadn't seen a pattern of clear abuse in other states, I'd agree with you.
But the record of states that don't have explicit posting requirements is clear - if we give business owners the choice, the signs will be small, illegible, and in locations where no one can see them.
Here in Florida, we don't have to worry about all this nonsense, since a "no guns" sign has no legal backing whatsoever.