Once I've done all the horn inserts, and cut and sanded the string nock, I fit the head then do about 3 coats of Danish Oil (beeswax, boiled linseed oil and turpentine mixture - probably the same stuff as Tru Oil?) all the way up the shaft, so I do the whole lot.
I then glue the fletchings on, over the Danish Oil using superglue usually, then whip with silk starting at the base of the fletching. I always whip all of mine all the way up, then finish at the nock end with a dab of superglue again.
At this stage, I then paint PVA glue over the shaftment and whipping, doesn't really matter if you get it on the feathers as it's clear anyway. Once the PVA has completely dried (I usually leave it a day) I go over it with actual varnish (not the Danish Oil) that dries clear. I've found that using Danish Oil on its own doesn't do a whole lot to keep the whippings in place if they really want to come undone, say you get a through-and-through on a target, or it goes into the ground and drives along the grass etc, they'll come undone if not properly glued in place. As you say, the PVA turns white if it gets wet, so that's why I go over the dried glue with proper varnish at the end - something like yacht varnish works really well.
