Genitals Guinea pig's penis is red

The tip of the penis is usually quite red due to the blood flow to that area. I have no idea how red your boy's penis actually is, so I can't tell you if it is normal or not.

Obviously the video in the sticky on this forum regarding boar cleaning shows the penis exposed but it isn't a high enough quality to really see it properly. Here is a short video where a penis is exposed, I consider the penis in this video to be very normal so perhaps you could use it for reference.
https://www.youtube.com/watch?v=BVfE1EOYQRo