Well, I don't think that there are particular colors that are rare. What u need to realize is that some are more vibrantly colored than others and some have more contrasting colors than others. In my opnion a fish that is lighter blue and fades towards darker blue is not as exciting as a green fish which had red in its fins. Realize that pet stores get lots of them in every week and every week they will have a different variety. Rather than being set on buying your fish on that one day, you might be better off visiting a couple of your LFS a couple of times over a week (they usually all get new shipments in at least once a week) and check out your options. Sooner or later u will see a fish that just "wow"s u. I have been in my LFS and seen nothing than plain looking fish and then gone back 3 days later and seen the most stunning beauties. U might also want to get familiar with the different types and see which one u find the most beautiful. I personally love the veil tails and the crowntails. I don't like the halfmoons, etc. Also if u check repeatedly, u will get there once just after their shipment came in and get healthier fish. I got my
Fish for example in perfect condition.
And I had been to the same store 2 days prior and he had not been there. I saw all the fish they had with fin rot and this being my first betta, I was not gonna buy a sick fish b4 I even learned how to take care of a healthy one. I kept checking in the LFS and looking for fish that had impressive colors and then make sure they were active and the ends of their fins were not frayed. I found one and bought him and he has been doing GREAT for 6-8 weks with no sickness or anything.
I
have also found that if u spend a few minutes with the fish u r considering to buy, u will get a basic idea of their temperament.
For eample 2 months ago I bought 3 Betta (2 for a friend and one for myself). The first one I bought was deep red crowntail with pink spots on his body. I found the combination very unusal and got him for my friend who had wanted a betta fish. He turned out very friendly and my friend loved him so much, she wanted another one. One day when I happened to be in a petstore for something else, I happened to see this INCREDIBLE crowntail. He was bright turquois/blue with a dark face and red on his fins. He was in his container with his fins spread out (not flaring, but just spread out) and was just breathtaking. Everytime u moved the container closer to me he raced to the opposite side. He was very scared but looked soo beautiful with his spread fins, that we decided to get him. And at home he ended up being just as in the store. You can admire him from afar and he just floats there with his fins spread out (I have never seen any other betta do this) but if u come close, he runs and hides. After that I swore myself that the fish I was gonna get for myself was NOT gonna be a "scaredy cat". So when I looked for my fish, I not only looked for color (ended up with one that is blue/purple - my favorite color), the state of their fins, etc (except for a couple of kinks, his were perfect) but also checked how the fish reacted to me. Mine won me over by swimming towards the back, but then coming right back and checking ME out intently. Well - it was love at first sight and in his new home, he is just like that. Every time the door opens he eagerly swims to the front to see who came in. He is not shy at all and watches with rapt attention anything that happens near his bowl. He wins over everone's heart and he is so vibrant that I have made many a betta owner jealous ... Anyways - my point is, there ARE gorgeous and relatively healthy bettas out there, so don't settle for a fish u think is "nice" and then find yourself buying food for your fish a week later and start kicking yourself because u see a "stunner". Unless u r ready to start up more and more betta tanks ... Anyways, that's just what I experienced. Due to various reasons I have actually bought a total of 5 or 6 be
ttas over the past 3 months (for various people). I decided to put my foot down and not buy a fish that already had fin rot or torn fins and sticking to this all bettas I bought did GREAT in their new homes as ong as there was no gross neglect from their owner. Of course u might fall in love with a particular fish and want to take him despite imperfections and fix him up. I'm sure lots of people on this forum could help with that. Sorry for my ramblings, but I thought u might find some of this helpful.
ill buy a 2 gallon as a temporary tank, and when i get home, ill put him in a 5. Im going to my lfs today, and every other day , to check out the bettas. To make sure I get a handsom betta. I want to get a crown tail... but, i dont know. it depends on what other colors of other species(i waant a purple one,those are really cool) anyways, Thanks! 
