white with random black spots is a very classic sign of a dominant white crossed with a colored chicken.
white leghorns have dominant white. you used a black roo.
do the math.......
looking at picture again, noticed several of them including the light one seem to have yellow skin. are you sure that roo is a black orp? as yellow skin is a recessive gene, so chicks with yellow skin can only happen if both parents are at very least, carriers for it. orps have white skin so if he was really a black orp all chicks should have white skin, including the light colored one.
suspect some of the dark ones are from sex links as they show some brown plus tell tale signs of yellow skin. if this is correct then thats even more proof the roo is either not black orp or if black orp then he's a carrier for yellow skin. (check his soles and webbing between toes, if they are yellow/orangish he is yellow skinned. if white/flesh clored then he's white skinned)
p.s.s. forgot you mentioned buffs. some lines have dominant white, it helps to get rid of any trace of black in the buff feathers. if the chick is half buff instead of leghorn, it will molt out to lots of buff showing through on the white feathers. if the feathers stay mostly crisp white with either no or few black spots would hold to leghorn mother.
