Oh, i think she is cute like that too.
Um, how do a pony get regrind? Im not sure what it means.
Its simply a breakdown of the plastic. Regrind plastic is plastic which has been made from the melting/moulding of recycled plastic [previously used plastic ground into pellets]. Its much less stable than a mould made from new plastic. It breaks down and separates much quicker due to it having an earlier cure date [i.e. the regrind is "older" than the new plastic]. You can see this kind of discolouration [yellows and pinks] in other plastic products which use regrind plastic - especially in plastic which is regularly damp for some reason - its surprisingly common on plastic baths and shower basins around plug holes - that odd pink or yellow tinge of colour.
We call it regrind because that's the type of plastic which causes the problem.