After Bart and Milhouse both taste the Squishee, Bart has a Squishee mustache. In the next shot, Bart's mustache has disappeared without him licking it off.
The color of the Squishees changes as Apu is getting the boys' Super Squishee. Before Bart hands over the money, the Squishees are purple and red. The next shot of the machine only shows a purple one (Apu is blocking the red one.) As Apu is taking the cup over, they both loom purple. Apu starts dispensing green Squishee out of the left nozzle. Once he is finished, the left tank shows purple, and the right one shows green. The Squishee the boys has is consistently green.