Was the leather veg-tanned?
How did you apply the Hi-Lite was the leather damp or dry I have better luck with water based stain if its a little damp, make sure the finish is water based if you are going to rub it on. If you’re going to spray it on do what immiketoo suggested let it dry then buff.
If I’m going to use a Hi-liter I normally use a dye first then put the hi-liter on this gives the piece a contrasting look between light and dark. If I want to bring out the grain of the leather and add some contrast I apply something like Super-Shene first then I hi-lite to enhance the tooling rubbing it into the tooling and cuts then wipe it off, the Super-Shene or what ever sealer you used will protect the high areas from taking the die. I think the key is to wipe not rub you want to remove the hi-liter from the top but leave it in the tooled and cut areas.
From Tandy’s site
Eco-Flo Hi-Lite is water based, low V.O.C., light stain for use on natural veg-tanned tooling leather that will bring out and enhance cuts and impressions.
Also you may want to check out the Dyes, Antiques, Stains, Glues, Waxes, Finishes and Conditioners forum.
Doug