All of the offspring will be solid coloured and most with bibs. The males will be either blue or black and the females either chocolate or lilac. The females will be that colour because Welsh Harlequins have two chocolate or brown dilution genes that are recessive and sex linked. The offspring will all have one dose of this gene but it will only show in the females (black diluted to chocolate and blue diluted to lilac).
They will possibly be a little smaller than Swedish in sise but I'm just guessing on that. How well they lay depends on the parents rather than the breed. I have two Swedish that are incredible layers and two that are very ordinary.