The blue....they came out with the black right after i bought it, to my chagrin at the time, but honestly, I like the blue now, it has a certain 'panache'...
I went with the blue SP1000M as well. It's different than the standard DAP colors of black, dark gray and silver.
Currently I'm using the black A&K case that came with it. But am looking at a blue case in the future. I also noticed that A&K just released leather cases for the SP1000M in three colors - gray, dark blue and blue
https://us.astellnkern.com/collections/accessories/products/a-ultima-sp1000m-case