I had a "lavender" coloured chick turn up in a clutch of bantam eggs i set under one of my hens once.The line it occured in i had been breeding for arounf 5 years.
All my banties were black or brown or gold flecked (i bred for colours not show) so i was puzzled as to were the colour came from.
She did reproduce another "lavender" colour and also a white chick when mated to an unrelated black rooster.
They in turn reproduced white and lavender splash chicks when put to another black roo