Yellow pea seedling

I’m growing some mange tout this year (Shiraz(, some planted direct and some inside in toilet roll inserts and planted out later. The direct sown ones took a little bit longer to germinate, as expected, but most are through now. Just one of the seedlings is, however, yellow. It was yellow as it emerged, rather than turning yellow afterwards, and it appears to be growing ok so far. I presume it will run out of steam at some stage as it won’t be able to photosynthesise, and I’ll probably just pull it out anyway. Any ideas as to the cause? Just a genetic anomaly, analogous to albinism? Or some sort of pest or disease? Never saw it before.
Thanks