Underexposed misuse

Back in 2010 I visited a garage sale and found a Canon T50 including some lenses and a flash for just 20 Euro. It's owner proudly showed an already used film and told me, that he wouldn't know whats inside but I could have it, too. I put it into the camera bag and forgot about it... Now - back into lomo addiction - I took a look at all my stuff and found that film again. I thought about giving it to the photo laboratory, but I wasn't sure if there's anything usable... so I decided to open the can, make a redscale and expose it again. This was the first time I turned a film by myself. It finally worked, but I didn't thought about ISO settings, so the whole film is underexposed. Whatever, I learned that underexposed redscale film can turn to purple colors... haha... strange thing.