desert tortoise with first slight pink urine

I have had my two desert tortoises since they were
under one-years-of-age. There fifteen-years-old now
and have been very healthy. For the first time today
I noticed that one of my tortoise's urine was a light
pink color. I also am so confused on what toxic
plants not to feed them. I read two different
articles. One did not put down impatients as a toxic
plant, so I have fed my tortoises these flowers.Then
today I found an article saying do not feed impatients
to desert tortoises "poisionous." Could this be the
cause of the slight pink tinge in the urine?

Thank you,
Christine