Splash Maran Roo + Rhode Island Red Hen = ???

The splash Maran is extended black with two copies of the Blue dilute gene. Extended black is very dominant gene that will cover most other pattern genes. It will also cover that red base color completely. Your splash should produce Blue chicks with the RIR hen. The cockerels will have lots of red leakage as they mature.
Leghorns are dominant white. That means they are a solid black bird with the 'white' gene modifying black coloring, turning the bird white. Since the white gene only affects black coloring, and the splash rooster is basically a solid black bird, there is a good chance you will get white chicks from that pairing.

 

My take on it is....

Splash roo with RIR hen, blue chicks. Red leakage may happen.

Splash roo with Leghorn (dominant white), all white chicks (yellow down).

LofMc

 

Well, from what I've read, Bluebells are popular in the UK, and are a hybrid mixture of RIR and the right color of Marans (splash or blue) to get the blue colored Marans/RIR hybrid chicks known as Bluebells.

If you had used a Cuckoo Marans, you would have ended up with speckled coloring (cuckooing) and would have created a Speckledy, again a UK hybrid. (If you had used the hen as the Cuckoo Marans with a RIR rooster, you would also create sex links.)

So, yes, with the RIR and Splash Marans, you've created a backyard Bluebell.

Splash is the only color that will consistently create blue. If you had used a blue feathered bird, you would have gotten 50% black and 50% blue (as the coin is tossed averaging).

LofMc

 

I'm sure they'll be pretty.

I've got an egg (for a test project) under a broody right now which is Double Laced Barnevelder roo over Splash Marans....I *should* get a blue laced dark layer. If this goes well, I'll set more with the next broody as my Splash Marans is still pretty young and still laying smaller pullet eggs (not the ideal to set).

LofMc

 

They are adorable!