is the paint coat covered under the lifetime warranty?
It's not paint. It's a dye. Even so, it usually doesn't hold up unless you take it easy with it. I've got a mini 2 pc. Santa Cruz (gunmetal) and have used it and cleaned it quite a bit. It still looks new but doesn't get banged around at all and I just use rubbing alcohol and a toothbrush to clean. I prefer not to try and test the finish by intentionally scratching it, but I do think it'll hold up and continue to look good if I use it and clean it as I have so far.
"Aluminium anodizing is usually performed in an acid solution which slowly dissolves the aluminium oxide. The acid action is balanced with the oxidation rate to form a coating with nanopores, 10-150 nm in diameter.[6] These pores are what allow the electrolyte solution and current to reach the aluminium substrate and continue growing the coating to greater thickness beyond what is produced by autopassivation.[8] However, these same pores will later permit air or water to reach the substrate and initiate corrosion if not sealed. They are often filled with colored dyes and/or corrosion inhibitors before sealing. Because the dye is only superficial, the underlying oxide may continue to provide corrosion protection even if minor wear and scratches may break through the dyed layer."
http://en.wikipedia.org/wiki/Anodizing
You can get some colors from anodizing without dyes (organic acid anodizing), but not bright colors. I'm pretty sure this organic process was used on the only 2 brands I've seen (MixnBall and Titan) where the anodizing definitely holds up to anything but digging at the finish (although I haven't used any harsh chemicals to clean either).
"Anodizing can produce yellowish integral colors without dyes if it is carried out in weak acids with high voltages, high current densities, and strong refrigeration.
[6] Shades of color are restricted to a range which includes pale yellow, gold, deep bronze, brown, grey, and black. Some advanced variations can produce a white coating with 80% reflectivity. The shade of color produced is sensitive to variations in the metallurgy of the underlying alloy and cannot be reproduced consistently."
From what I've seen, if you want one of the popular brands in a colored grinder, and want it the looks to hold up, you have to treat it gently (including the cleaning process), and that may even include avoiding all but the very smallest stems when you grind. A non anodized grinder will last just as long (in real world grinding) and scratches won't show as much, so it's easier to have it looking good long term, vs. colored anodized models. Corrosion should not be an issue with grinders, so IMO anodizing is mostly more marketing gimmick than a useful process for protection or strength.