A bit of a guess (but it makes sense to me, anyway!):
White lambs will grow into white sheep, from which wool can be obtained that can easily be dyed to any colour.
Black lambs would grow into black sheep, where the wool wouldn't be as suitable for dying. So most of those cute little black lambs are probably destined to be accompanied by mint sauce.
In the field below my window there are about 3 dozen sheep most with lambs, there is a really cute all black lamb and it's mother looks sort of a dark grey colour; slipped through the net perhaps?
black sheep of the familly are usually into crime such as rape, murder and organised crime. It is only common sense that their life span is a lot less than normal sheep
I mainly walk my dog on a landscaped pit tip and the forestry commision often have flocks of sheep grazing on them, but they are all black. I cann't remember the breed of sheep but when I questioned one of the rangers I was told this particular breed of sheep was often used on reclaimed tips as they thrived on the rough vegitation growing on them and quickly "Leeched" at lot of the acid produced by old mine waste oput of the system, as one of the first stages of fully reclaiming the land. Apparently they have quite a few of these sheep and they rotate them round all the local tips
Could be any one of the following : Welsh Black Mountain, Torwen or Balwen. Torwens & Balwens have white faces or underbellies respectively.
In answer to the original question, most of the lambs bred in spring will get eaten (by us, not the wildlife), except those that are kept on as breeding stock. As white sheep are much more common than black ones, it goes without saying that there will be more of them!!