After a number of years experimenting with blends, we have found it very difficult to produce a consistent yellow plastic without introducing what, to us, is an unacceptable amount of virgin material into the mixture. This has led us switching to a bright lime colour, similar to that used on hi-viz jackets, as our alternative. So far, this has gone down very well with our customers.
We are not in a position to comment on the amounts of virgin plastic used by other companies in the production of their yellow. Perhaps you can ask them yourselves.