Turn someone’s water blue (or red, for a more horrifying effect).

“Sweetie, will you go fix the leak in the sink?”

Fill up a pitcher with some “orange juice” (AKA the powder from a box of mac and cheese: it’s the exact same color!)

Replace someone’s deodorant with butter (or cream cheese).

Squirt a few drops of food coloring onto someone’s toothpaste to temporarily recolor their pearly whites.