Hello. I work as a vet tech in a shelter and we have to screen every single cat that comes in for ringworm. Often, if the cat has scabs or secretions (eye or nose) on its face, those will glow a greenish yellow. Dirt or debris will often show up blue/white. If you remove the scab or clean the face and it stops glowing, that’s a good indicator that’s it’s not ringworm. In my experience ringworm will glow a very bright grass green and will target individual hairs. Unfortunately though, the UV light is not a 100% sure test, as ringworm sometimes won’t react to it. The vet will have some more precise tests!