Splash is more of a yellowish to grayish-white color in chick down, more easily mistaken for White than for Blue in my experience. Blue can be pretty light gray, but generally not as light as Splash. Here are some Splash Cochins as an example:
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Splash next to a lighter Blue (plus another darker Blue on the right) :
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These are some of the lighter Blues I've hatched, but they're still definitely grayish rather than whitish or yellowish like the Splashes:
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If you still aren't sure by down color, then you can always wait a bit for some feathers to come in and give you your answer. Mostly white feathers means Splash, blue-gray is Blue, of course.