I suggest you start reading.
has great articles on genetics and breeding
For foundation stock you want high quality animals. If there is an IBC affliated group around where you live I highly suggest you join. They can provide much insight and many groups hold shows where you can get high quality stock at low prices. I also suggest you join the IBC to learn more.
You can search for groups and investigate joining the IBC by going to www.ibcbettas.org
As for what tail types or colors to choose.. that is up to you. Personally I would pick a tail type that is popular among breeders. Namely Halfmoons and Plakats.
Many people on this board believe breeding pet store fish is ok. I'm not one of those persons. There are way too many variables when it comes to pet store fish that make them unsuitable for breeding, they can be rife with genetic issues that can be passed along to the fry, not to mention most pet store fish are basically mutts.. not great for perfecting the betta.
I would try to get a sibling pair to start with. That is your best bet of ensuring that you get the phenotypes you want.
Above all, the best piece of information I can give you is don't breed just for color. Color should be the SECOND thing you look for. Form and finage should be the first. Color is subjective. A well put together fish is what will help to perfect betta strains.