Chemical GuysCly_402 Medium Clay Bar, Grey - 100 gm

What is the difference between light, medium and heavy clay bars

The yellow clay bar didn't get paint scratches off. Does gray one work better for this?

Will this remove tar and asphalt sealant? Has anyone had this problem? I'm being told washing and buffing may not be enough to remove it.

I have new headlights (plastic) that have overspray from car paint. Will this bar be suitable to remove without losing the shine and newness?