I Urinated Dark Brown/reddish Urine 2x Tonight After I Was

I urinated dark brown/reddish urine 2x tonight after I was running on the treadmill for about 30 minutes. In the last 10 minutes I had the urge to urinate but I held it until I was done. When I finally went to the bathroom, that's when I noticed the color of my urine was not yellow or clear. It wasn't painful. There was no odor. Went to the store and urinated again. Same thing, dark colored urine. Drank a lot of water on the way home. Urinated and my color changed back to yellow. So was it just merely a case of dehydration or do I need to see a doctor to see if I have an infection or something else?