|I would very much doubt that you would have bald spots right away, unless bleach were applied directly to the diapers. It's possible that down the road you might see a few spots, as anecdotally from this forum, it seems that the bamboo do worse with bleach that the cotton, but what's done is done, right? I just would do everything you can to make sure no bleach gets on the bamboo esp.
As far as the color of them, one thing I'll say is that over time, my unbleached diapers ended up whitening, and the few bleached ones I had darkened just a bit, so they are indistinguisable from each other, though they started out "natural" and snowy white. They have all spent time in the sun, so maybe that sped the process with the unbleached. I have only one bamboo and it hasn't had much use or sun, but I think that it has probably also lightened a bit, just over the course of washing.
If you are looking for something to use instead of bleach when your son has diarrhea, you might consider something like tea tree oil. It has disinfecting properties (probably not as thorough as bleach, but likely enough for your purposes) without the caustic side effects. Personally, I probably wouldn't bother doing anything out of the ordinary unless I had reason to think that the diapers were re-infecting my LO. If an older child had diarrhea and didn't make it to the toilet, parents probably wouldn't bleach his underwear and clothes, would they? Of course, knock on wood, we haven't had to deal with much of that, so maybe I just don't know . . .