There is a reddish colour in my rabbit's urine?

This can be a sign of stress or of something more serious such as a urinary tract infection or internal hemorrhaging. I would watch her for a few days and if it doesn't get better take her to the vet. Also, rabbits can get pregnant at 6 weeks old in some cases, so both of them might very well be pregnant right now. I would suggest moving them to their own individual hutches and waiting to see what happens. Also, rabbits do just fine outside. I have actually found that most of them do better because of the cooler environment and constant ventilation. As long as they have some where to get out of the elements like a solid part of a hutch or a dog house they are fine.