Wow what a jerk lol I've never had a guy not be okay with getting it on during a light period, but he must have thought it was something else? Was he using a condom? He's going to look like a complete idiot if he tries to say to anyone that he freaked bc he saw brown. "Dude, she was on her period. Chill."
If it makes you feel any better, I was seeing this guy I reeeeeeeeeallly liked over winter. We were at his place, fooling around, slept together. When he finished, he handed me a dirty white shirt to clean myself up with while he left the room. I realized a lot more was coming out than normal, turned on the lights, and saw that I had bled ALL OVER HIS SHIRT! I wanted to cry. I just kept thanking Jesus that his sheets were brown. He acted totally fine even though I'm sure it grossed him out and I just pitched it in a paper bag, but oh God I was so embarrassed.