A splotch is a messy or unevenly shaped spot. Some people get bright red splotches on their faces when they blush.
Be careful when you're eating something messy in your brand new shirt—you might end up with splotches of barbecue sauce or watermelon juice all over yourself. You can also use this informal word as a verb: "The artist began to splotch pink paint randomly across the canvas." Splotch first appeared around 1600, possibly from a combination of spot and blot. The similar splott in Old English meant "a patch of land."