Hello.. for a buff orpington roo, over cream legbar hen would they be sexable at hatch? Or would be too light to see white dot?
You won't know without trying

My Barnvelder (roo) over Cream Legbar (hen) produces wild type chipmunk every time, however I do get inconsistent head dotting....I've learned that if there is even a whisp of white on the head, it is likely male. My females are pure chipmunk with no white streaking whatsoever on the head.
You probably will get buff based on both chicks with a light dot on the head of the males, but you might luck out and get some faint wild type streaks as the CL has more than just barring in her genetics.
Hopefully someone can come on here who has done that combination.
LofMc