Your bag is natural vachetta leather. I saw one of these some months ago at
Nordstrom Rack, but in a smaller size, I believe. These hobos are very nice!!
Water, magic erasers or anything like that is bad news on vachetta. The reason is vachetta, or any vegetable tanned leather is not stable in water...it shrinks and eventually becomes brittle and can crack. I'm not saying it's not possible to do it and get away with this for "x" number of times, but I know someone that did this repeatedly with a LV bag, was out in the rain, etc, and ruined the handles (they are cracked now), and I can't fix it. I guess the bag can be restored. In any event, ANYTHING you do to it, conditioner, water, cleaning, will probably darken it. If you don't get it wet very evenly and lift the water very evenly, then it will look splotchy and you will have a mess. Honestly, I do not recommend this, and I would send any bag I loved to a leather restoration professional before I tried it too much. Also, if you do wet it, I would not wet it too much because remember that vachetta shrinks, and also it may have to be conditioned and buffed to restore it to it's natural shape. Usually the colored vachetta or vegetable tanned leather is easier to clean with a cloth because it doesn't stain as readily, etc.
Conditioner will also darken it, but TBH I've gotten away with conditioning and spraying some types of vachetta many times. It's easier to do that more evenly, especially if it's a less porous piece of leather. I can't see your bag in person, but I'm thinking it's more porous than my Dooney bag with vachetta trim. In that case, I would try to lightly remove the spot that's shown in the photo with tape (lightly so that you don't yank off part of the leather) and then rub it with your fingers. It will appear lighter/whiter after you lift the tape. This has worked for me. I use shipping tape, so I would go ever so lightly on it.
Honestly, vachetta is very hard to keep. Light, oil from your skin, etc will darken it over time, and sometimes the pieces do not darken to the same extent as others. It's just inherent to the leather. Whatever you choose to do, I would ultimately spray it with Shining Monkey. This spray IMO is the best for vachetta and keeps down on the patina, or at least promotes a more even one. It also makes it easier to remove any spots that get on the bag because it provides somewhat of a barrier. I would definitely spray the metallic too.
Maybe put some Apple conditioner on it, that may clean up some of the light stains you're referring to.
) for doggedly reminding us of this website. 
