Hi,
I'm not a regular user of canvas borders but have experimented with them in the past.
Is there a way to smooth or blur the color and the photo at the place they are come together? let say 5mm?
No, there isn't currently any way to do this.
I did some checks and wondered which type of canvas border you were using, mirror or stretch?
I noticed that the mirror version on the images I checked was much more subtle at the interface and corners than the stretch version. There is a definite diagonal "line" on the stretch version at the corners which should not be noticeable once the canvas is wrapped on the stretcher - providing it is done accurately.
Terry