so i have had my ducks for awhile and they were laying great until winter hit and days got shorter. they completly stopped and my chickens slowed down so i put up lights to get them laying again. the ducks have started again, but the eggs are stained black! i've been getting more eggs now but all them are stained black. the first one i got i washed off and it just turned slightly purple, as if i had dyed it for easter. we used it though and it was still good. what is wrong?!