Bright day
Could it be that black Petes are deviation of slavic Czerts (Lesser Devils), or vice versa? (Czerts or Cherts, are reason why all Czech and Slovak (and maybe Polish) kids quite fear evening before st. Nicholas day- he would then go from house to house with entourage of angels and these "lesser devils" seeking out children, while children would hide under beds and cupboards and in closets, and often had to forcefully presented to Mikulá).
But as far as I can tell, catholics have Christkid and Protestants st. Nicholas, some of the latter than would then move his day on Christsmas Day.