I have never showed them as Splash but this is a direct quote from "Old English Game Bantams as Bred and shown in the united states" by F.P. Jeffery and William Richardson consider by many to be one of the best books on old english.
Splash Old English
"Disqualifications-Any appearance of rust in any section of plumage-more than 50% blue in plumage.
Defects-Brassiness
He goes on to say
"For each blue variety(except self blue) there is a splash.These include Blue,Blue Red,Blue Brassy Back,Blue silver duckwing,blue golden duckwing,silver blue,lemon blue, and blue wheaten. All of the splashes coming from mating the various blue varietys are somewhat different so when using the term splash it is vital to know the breeding background of it. Splash breeds true in that splash x splash gives 100% splash.
Most exhibition splashes come from blue x blue mating or blue x splash mating but any splash which meets standard requirments, regardless of background can be shown as a splash."
I know they are used as tools in breeding programs,because that is the way the Splash(Sport) came about.