Residue only happens if the melt goes on way too long.
My timing for it is 8 Hotels.
I always use black heat shrink whatever the color of sleeve and I never get it breaking up and mixing with the sleeve.
Also, you're only supposed to be melting the shrink/sleeve sandwich over the wire crimp in the blue part of the flame, waiting to see the sleeve bubbling out of the shrink, so even in the highly unlikely case of any residue it would be completely out of sight.
As I remember it the thread to which I referred earlier went on for some time over complications arising out of the difficulty of doing it.
If Lutro0's 10mm method worries you you might consider the 4mm method I described in my first post.