When I masturbate with a showerhead, I squirt. Is that urine or real squirting? It’s never yellow.
Masturbation with a showerhead is a great thing, but in the case of your question it complicates my answer! I’m assuming that you’re masturbating with the water spray, which means there’s a lot of water involved, all around your body and possibly inside your vagina. This makes it harder to distinguish the color, consistency, and quantity of liquid that comes out of your body when you masturbate.
What I can say is that typically people don’t (involuntarily) pee when they’re having sex alone or with somebody else. Here are some things to consider in your personal investigation of the ejaculate-versus-urine question: Often, before squirting you can feel a tingling sensation similar to what you feel when you’re about to pee…but you won’t pee. If you keep going beyond that tingling sensation and ejaculate, try to find a way to look at the liquid that comes out. That’s where the shower context makes it hard investigate. In any case, the ejaculate liquid shouldn’t smell like pee; it’s more likely to be fragrance free or to smell like your vaginal fluid when you’re aroused. As for consistency, it’s closer to water and vaginal fluid than male ejaculate; it’s more liquid. Finally, the color should be on the scale of clear to white rather than yellow like urine. Good luck with your investigation!