ColorOops sounds like it works the same as ColorFix (which I've used) in that it lifts the cuticle and effectively "shrinks" the dye molecules so that they can be washed out.
Three *important* things to note when using a product like this:
1. Although it claims to restore your natural color, it *cannot* do so if you've used a lifting or permanent color. The way permanent color works, essentially, is by raising the cuticle and lifting your color -- turning the strand a pale brown or straw-like color, depending on your hair -- then depositing and developing the new pigment. This means that, using after a permanent color process will shrink the previously deposited color so it can be rinsed away *leaving the base pale brown or straw-like color*. So, if you've used permanent color IT IS IMPOSSIBLE TO RESTORE YOUR NATURAL COLOR without following the treatment, as mentioned, with another tint. If the color process you used lifted and/or deposited unevenly, ColorOops will remove it unevenly -- which is why the results frequently include splotches of different shades varying from aforementioned pale brown to straw-like color.
2. Because it shrinks the color molecule, you must then rinse it out. Any color that you do not rinse out WILL BE IMMEDIATELY REDEVELOPED once you try to color it again (or use the included solution, which I'll get to in a sec). For example, if you have too dark, permanent color that you're trying to be rid of in order to re-color a lighter shade, and you *don't* make sure that you've rinsed/washed enough, as soon as the developer from the new color hits your hair it will immediately return to the color you were trying to be rid of.
There should be a solution included, that you use on wet hair, after rinsing. Many people will suggest that you don't use it -- specifically for this reason (it frequently just undoes all the color removing you've just done). I will, however, suggest quite the opposite for the same reason -- using the after solution is the only way you can be sure that you've rinsed all the offending color away.
Speaking of rinsing, my own story: removing black dye (that I'd done for years) to go back to dark brown. 3 processes (not using the after solution), and THREE DAYS of rinsing/washing with Suave Clarifying -- while I had hideously straw-colored hair -- and it was still too dark, albeit mostly reddish. As soon as I tried bleach (because this process just wasn't working and was drying my hair), the developer re-developed and I was right back to black. I had to bleach it two more times to lighten it enough to re-tint. Needless to say, hair was in not-great shape for quite some time thereafter.
The moral of *my* story is that it took 3 days of multiple rinsings/harsh washings and it STILL hadn't removed all the color. Although i list my hair as being medium porosity, I think medium-low is probably more accurate. Having more porous hair may yield better results as the color will probably rinse out more easily.
3. If it's anything like ColorOops, it will require multiple treatments and yes, it *will* dry your hair.
If you do this, via con dios, friend. I've read so many reviews of people for whom this worked and I don't want to scare you out of doing it. Just know how it works and what you're getting into beforehand.