Changing a photo from black to Color

I took some photos using my Nikon D70. It was one of those moments that needed a quick grab the camera and shoot. Unfortunately I must have turned the mode dial either the last time I put my camera away or when I took it out to shoot. I usually keep my camera in Auto Mode but somehow it got turned to Portrait Mode when I took the photos. I was trying to take photos of a very rare large Ram on a rocky outcrop. It was standing tall very close to me and was magnificent. I was so excited to be able to capture such a rare photo. However, when I got home and downloaded the photos everyone was totally black. I noticed my camera was in Portrait Mode. Is there any way to save the photos, turning them from black to what should have been fantastic photos? My camera takes very sharp, crisp, vibrant color photos most of the time. Can they be saved???