the rib would be the seam, you can set it to random if you prefer, but there is no way to not have a seam.
Would you post a picture if you have the time with your color issues? i didn't experience that
It fits on mine perfectly. My other 2 designs are the same print and haven't had any issues.
I have heard some printers have slightly different sized metal pegs for the extruder visualizer. If you measure yours I can put one together for it.