Hi Helen. I would use fine grade fir bark mix for repotting the seedling and put it in a small (tiny) pot so that it's as root bound as possible. Keep a close eye on the moisture levels, it will probably mature a little faster if your grow it under moderately bright conditions (meaning avoid the direct sun). Btw, it might not be the same thing that it was growing with which may account for the different leaf colouration. Usually the seedling leaves of paphs are identical to their mature selves, at least according to my own experience thus far.
Vini does mean that it's a dark colour, but that can be effected by seedling variation and parentage.
In other words you can't really know what it looks like until it blooms unless it's a division off a dark vini parent then it would be identical to the 'mother'.
I'll post a picture of my suk if it ever opens..sigh...