Is there any reason for choosing Splash - This will be a French, feathered leg type, which I think occurs when breeding blue to blue, (I am only just getting into the breeding of the French type), and as far as I am aware it is not a colour recognized by any Marans Club anywhere in the world, but anyway certainly not in the UK, so perhaps the breeder is breeding for egg showing rather than showing birds.
If you are not particularly buying for the colour of the bird, why not ask your breeder, which of their birds they would recommend for dark eggs. It might also be worth asking about how many you can expect from each bird per week, as some strains of French Marans are not all that prolific The colour of the Marans egg is mostly "coated" on in the last stage before laying, and as this reserve of pigment runs out so the eggs become paler, hence poorer layers will sometimes produce the darker eggs, though infrequently. Similarly as the eggs become larger the pigment has to stretch further, and eggs loose the depth of colour.
Copper Black Marans have the reputation for producing darker eggs, but so much is down to strain rather than variety. Many of the better colour eggs are from recently imported stock from France and Belgium, the breeders here seeming to loose the egg colour rather quickly.
Wheaten have been the lastest to be imported in any numbers, and currently some of the Wheatens can be good dark egg layers.
Ask to see a tray of eggs so you can get a feel for the colour egg the parents are producing
Good luck with them Marans are lovely birds to keep and their eggs always cause such admiration. By the way you are looking for an egg with a good depth of shine as well, dull eggs are not acceptable in Marans circles.
There is lots of stuff on The Marans Club of Great Britain website, which has links though to an English translation of the Marans Club of France