I can't seem to find the link to the chart I used to use, so this is the best I can find. There's pics at the bottom of the page, with a bit of additional descriptions. I also believe @CEC is extremely knowledgeable with Avic morphs, so perhaps they will be of some help
While the different morphs would breed without creating a hybrid (since they're technically the same species), it's highly advised against because it muddies the gene pool and detriments the hobby. The different morphs are from different regions and have different characteristics, so mixing them makes it harder to identify a true morph from a mixed morph.
@PidderPeets Re: hybrid... we don't technically know this. The last revision was only done using cladistics, there was no genetic data. So while morphotype 6 for example MIGHT be the same species, it very well could be different.
@viper69 You're right, I shouldn't have made that statement. I said that based on the fact that they're currently considered the same species. I should've taken into consideration that they could still be due another revision. However, I stated that they shouldn't be crossbred, and I think that was the most important part