Actually I have good news about my own female oto. I saw mine in teh gravel and she'd recuperated her colour. It was just that I saw her against the background of her white food bowl, basking in the neon light - I think even I'd look near translucent in that sort of lighting conditions...
If yours is really pale even against slightly darker backgrounds, then it may be worrying. They quote stress as main reason on the articles I've read. They also explain that stress could be from unsuitable water conditions such as n'ites/a'nia, or even high n'ates. Unsuitable temperature, aggression from other fish, unvaried diet (what does yours eat? Does your tank have any algae? I'd suggest you try an algae farm if it doesn't. Check here for a description
http://www.fishlore.com/Forum/index.php?topic=10896.0), lack of hiding places or lack of other fish to school with. I know it's a long list, but I'd start looking at diet.