This is so confusing cause I don't own a delaware or anything that looks like one I got the egg to experiment with from eggs my chickens had laid.
I have a BO roo, 2 BO Hens, 1 EE Rumples Hen who only lays blue eggs, 2 BR Pullets, 1 CM Hen all of these are exposed to the BO Roo.
I set 5 eggs on July 20th, this little guy was born Monday at 6 AM the other eggs didn't make it all the way 2 was clear, the others 2 died before hatching.
The egg it hatched from was brown so I can rule out my EE I believe.
Leaving it to only 4 other suspects 2 BO and 2 BR pullets.
Oh and PS...the egg color was to light of a brown to come from my Maran she lays really dark eggs compared to the BO