[FMadera]

I've had that combination in person, having reffed Kansas in the past. I assure you, in person, they are no problem whatsoever, and I'm more stringent on contrast than most referees.

I wouldn't trust how things look on TV and assume that's how they look in person. The filters, lighting, etc., can make what appears on the broadcast look quite different than the in-person naked eye sees.

As far as contrast goes, if you take the color of one jersey, give it the number color of the other jersey, and can see it easily without a border around the number, that's almost always because...the colors contrast. If they're legal for the numbers, then they're legal as libero combinations.