My "mix" project has been going on for five years now and is called "Aloha Chickens".
What it is: Before Greenfire Farms imported Swedish Flowers, I saw them on Feathersite.com and loved them! But at that time, there were no Swedish Flowers in the US to buy. After realizing I didn't have the money to import them, I started trying to breed something like them, myself.
As you guys know, Swedish Flower are mottled, but in many colors. I had a hard time getting those colors from just Speckled Sussex (dark brown mottled) and Exchequer Leghorn (black mottled) as those dark colors tend to "overwhelm" the gold and red colors. That's when I found this really strange hen in my neighbor's flock. They were Hispanic, and did not speak english, so I was not able to get any info on where they got her. She was Banty sized, and appeared Mottled. When bred to an Exchequer Leghorn x Speckled Sussex roo, she gave me a few chicks to work with that had "new" colors. (Unfortunately, every single egg she laid after that was infertile, I tried to hatch ALL of them and had no more luck.)
From four very unique chicks of hers, I have created a new breed by taking those and mixing with Sussex, then NHR, and more recently, Buff Rock, and finally, "real" Swedish Flower. They ARE breeding true. However, since the foundation hen was a Bantam, the size tends to revert back to small when they become too closely bred for color.
Currently, I am trying to work out the size issue and get them breeding true for color again, while adding in the needed genes for size. It's slow going! Some chicks are bigger (in certain cases, almost as big as a pure Sussex or Swedish Flower) while others revert back to a small, somewhat "gamey" body type. The small size I understand, but the gamey type is peculiar, as the foundation Banty was small and round, not gamey at all. My only thought is perhaps, since Game chickens are popular with many of my Mexican neighbors, and Mottling is found in many Game lines, that perhaps that is where the foundation hen got all that mottled color. (I have also had the rare "Pumpkin" color seen in the Pumpkin Hulsey Game lines appear in my stock.)
However, the original chickens showed NO aggression. Later, a few random roos showed aggression here and there, and anyone showing that was culled. So today, I'm left with a very smart, tough, hardy, small standard chicken. Multiple roos can be kept in the same pen, and feather pecking in chicks or cannibalism or fighting in adults is extremely rare. (Haven't seen it in years, knock on wood.)
Goal is to get them up to full size, same as a Speckled Sussex or pure Swedish Flower, but would be in more colors than what is offered in either breed. Still working on leg color, needs to be yellow on finished breed but that is fairly minor. Had issues with odd combs, and puffy cheeks, and those still pop up from time to time, but goal is clean faces and upright single combs. Overall, body type is to be similar to Swedish Flower or a Sussex with yellow legs. Tail should be long and flowing on males, and I'd like to keep the cute upright "Fan Tail" seen on most of the hens but it's going to be tough!
Very much a work in progress but they are really nice chickens and I would call them more of a unique breed at this point than a mix. Will take a while to get them uniform for all traits.

This rooster (above) contains NO SWEDISH FLOWER bloodlines. He is the closest to the standard that I've bred so far. He needs a longer tail but that's it.
The BELOW rooster is an Aloha x Swedish Flower mix. Notice how he does NOT look like a pure Swedish, or a pure Sussex. Color is unique to this breed - he has much more white in the neck and back than either Sussex or Swedish. He does have a bit of Sussex (at least 1/8th) so that helped size, too. He is almost as big as a Swedish, just a touch smaller, but size is overall very good. Tail/comb are great, but he needs yellow legs:

Here is yet another Swedish Flower x Aloha mix. He is by one of my "oldest" bloodline Alohas. Therefore, he has more of the "gamey" type, smaller size of the foundation bloodlines. Also has white legs like his Mom. Overall, he reverts back to the pure "Aloha" lines more than the Swedish lines. Note his color is also unlike any Swedish Flower. I'm hoping to basically transfer his color onto a Swedish Flower:

The small hens are usually the most colorful.

The two "solid" buff hens are part Buff Rock, used to improve size. You can see how they are bigger. They carry the same spots but since the gene is recessive it does not show on the first generation. They are being bred to colorful roos to try and draw the color out again. The small colorful hens are being bred to a pure Swedish Flower right now, for ultra-spotty and colorful bigger chicks.
You can read all about the project here:
http://www.backyardchickens.com/a/the-aloha-chicken-project
I have started experimenting with shipping Live chicks and will be doing so again this spring. Planning on selling a box of 25 chicks for $100 postpaid due to using "Express" Mail. (I know technically I could ship Priority and they would probably survive, but I've been going Express just to be safe!) Trying to get these into breeder homes who might want to continue the line. I think now it could be a nice compliment to the Swedish Flowers. It's just an American version of Swedish Flowers, after all!