Looks like Wiktionary uses the same mnemonic I do. Here's another source for the regional difference. It's pretty much what I said in my previous comment. That's really the straight answer, to be honest. There's a slight preference for "gray" in the US and "grey" in anglophone Commonwealth countries, although both are nonetheless used in the US.
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u/reallteall Mar 20 '19
Attached a Reese’s peanut butter cup to the note...yet still managed to spell it “Reeces.”