I'd take that to mean black leather shoes that cover the whole foot (so if you dropped a needle on your foot it wouldn't go through). Ones without loads of seams and details are easier to wipe clean should they get soiled. You probably would need a flat, rubber sole that wouldn't mark floors. I have two pairs of black leather Vans, slip on and lace up versions which are fine.
From experience, even in hospitals people don't tend to stick to the shoe rules but quickly regret it when they get something gross spilt on them...