Please, watch this
http://www.youtube.com/watch?v=KLIPnToF1To This is what can happen to unwanted dogs. IMO you'd be better of putting your research into ways that you can help the existing mongrols in rescue become more desirable. After all, if you're concern is about the pricing of them, rescues represent a bargain!
I'm not against first time breeders, every one has to start somewhere and I suppose if you're going to do something wrong at least do it right so good for asking, but your questions concern colours, and what breeds would be a good idea, like it's just bit of fun to 'see what happens'. You should be serious about breeding not about experimenting. It's almost coming off like a God complex of creating something new and different. You should be first researching the process.
You sound very young/immature so i'm going to put it in such a way. If someone came to you with box, their experiment, said, 'put your hand in and pull something out. It could be the world's greatest puppy and a cheque for £1000 or it could be a death warrant for your dog, a deaf, blind puppy, a bill for £3000 and 2 months hard labour, or anywhere in between, the odds are 20/1' What would you do?
Of course all breeding has risks but breeding in the correct way makes these odds much more favourable. Espically as a first time breeder your designs (cross breeding/basing on colour/not understanding health testing) increase the odds of problems 100x. No matter what there will always be a huge unknown in cross breeding even if all else is good.
If you want to think about breeding i'm not going to criticise you, i'm sure we've all done it, I know I have, but get the silly ideas out of your head and start with the simple basics, not colours and compatabile breeds but the process from start to finish of breeding 2 healthy, health tested dogs.