Maybe. What color egg did the Splash lay? What genetics did the rooster inherit from the different parents? What genetics will the rooster pass on to his chicks? It will be different for each chick.
Not all Marans lay that dark chocolate egg. The breeders have to select for the dark egg color or the egg color will lighten over time. They will still probably be quite a bit darker than the eggs from other breeds, but they may not be as dark as you would expect. If the Splash lays a real dark egg and the rooster's father was hatched from a real dark egg, you have a reasonable chance of getting a nice dark egg.
But that Barred Rock will contribute genes to the gene pool for lighter eggs. So your rooster should have some genes for darker eggs and some genes for lighter eggs. The way I understand it, there are different genes that contribute to egg shell color. Since the rooster has mixed genes and he is as likely to pass on "lighter" genes as "darker" genes, you will probably get a mix of egg colors from different offspring. Depending on how dark the parents or grandparents eggs were, I would expect you to get reasonably dark eggs, but there is no guarantee and there may be some variety.
