I read somewhere that there are 14 mutations so far, I wouldnt mind mentioning them if you want. Hope that helped

 

Here's a mutations timeline: http://talkcockatiels.com/showthread.php?t=15332 It lists 14 US mutations and 9 mutations that are unique to Australia. It doesn't mention non-sexlinked lutino, which is a European mutation and an allele of fallow (meaning that they're different variations of the same gene).

 

P.S. There's also the infamous 'spot gene' which is not recognized as a mutation and isn't well understood by anyone. You'll find more talk about it on this forum than you will anywhere else. A variety of other oddities have been observed too (like the tricolor cockatiel, see http://www.littlefeatheredbuddies.com/info/breed-schimmel.html ) but these oddities are either not reproducible or don't reproduce consistently enough to call them a mutation. The e-book that srtiels wrote has pictures of some of these oddities. http://www.amazon.com/Cockatiel-Mutations-A-Bounty-Color-ebook/dp/B009IRGLWC/

Here are a couple of my spot gene babies. They are NOT pearl and don't have markings on their back and wings: