The brown pixels on Tails he's had since his inclusion of SRB2 are clearly fixed in the shots shown here, and in IRC. They likely did this through SLADE's repaletting tool though, since unlike Sonic's greys, Brown isn't used elsewhere on his sprites.
Even though it'd take long, it'd be worth it if it were me, just to stop the OCD that's been plaguing me for 7 years or so. Although the devs are hard at work with things, I'm pretty sure the new build has most of its planned features done besides the netcode fix, so the spriters likely have free time on their hands (besides Eggscalibur who I hear looks too much like an eggmobile). I'm not saying they need to do the grey pixels once and for all, but I hear the argument that "they could be doing something more important" all the time. In reality, like how developing stuff goes, there's always a time where some of the staff is probably just sitting around, this is usually the time where polish can be done on the little things or else they never get done.
Also, I'm pretty sure most of the users here have been playing SRB2 for years, existing since final demo isn't really impressive.