A search that led some lost Google soul here made me think of this tale from Gary's childhood.
Gary and his two sisters were under ten at the time. One day, they were playing in the yard with their black Labrador, Happy. Happy was in high dog spirits that day, and the kids were chasing him around, playing.
Then suddenly, their screams turned to screams of horror. Karen began to cry. Gary ran in to tell his Mom that something was wrong with Happy's "thing."
Wilma came out to view the state of Happy's penis, and found that it had a red protruding growth a third the length of the dog. Happy was still jumping about and kept jumping on the kids. "Eeeeeeeeeeee! He's touching me with it! EEEeeeeeeeEEEE!"
"It looked like lipstick," Wilma will say to this day. "I'd never seen anything like that. And the kids were screaming, and Ken was at work."
So of course, Happy had to be driven to the vet and diagnosed. Just to express the level of hysteria, Wilma drove only rarely, and stopped driving soon after. But the dog was obviously really sick, and the kids were crying.
Happily, no biopsy was needed, and the dog was diagnosed with a penis.
That's why I understand why someone Googled "Red + dog penis." (And I am proud to have been one of the few R-rated results. X-rated dog sex is popular.) I can easily see myself doing the same thing. My experience of the erect penis is limited, but Gary's doesn't look like that. Dogs are so open about their erections, and they have them even if they've been neutered, so "Penis" wouldn't have been my first guess either.