I purchased a couple of ice cube trays online and made rainbow ice for Pride.
I bought the trays on Amazon. The Hutzler 324 Ball Ice Tray makes 1-inch sized ice balls. It seems pretty good so far though I'm not certain of its longevity.
The Mydio 40 Tray makes small marble-sized ice balls of about half an inch in diameter. It's made of high-quality silicone and seems super sturdy.
Neither make clear ice (that's my jam, as you know), but the size of ice they make is very fun.
Then I just stacked them up in a glass in rainbow order. Silly, fun.