White Wine at the Seder

Sholom all,
I was wondering if anyone had more information about the custom to use white wine at the seder? I saw in the Madrich Minhogim the single sentence:
לארבע כוסות מהדרים אחר יין אדום, ולא לוקחים יין לבן כמנהג המקומות שחששו לעלילות דם

Is that all there is to it? In particular I'm wondering if the fact that the best wines from Germany were generally whites (mainly Riesling, which was highly renowned), if this could have also contributed to using them for seder.

Thanks!

Mishna berurah says that its because of the threat of blood libels. Additionally it may be that white wine was considered to be better quality. (it is nothing to do with Germany but with a general halachic issue among all Europeans.