Here's how I do it, others might have ideas:
Priority one: clean out the scratch thoroughly with acetone.
You can spend money getting flake from mini craft or other suppliers, on scratches, I use a close match glitter nail polish. Yeah really.
Carefully dab in the polish with a tooth pick until you've covered the white, then use a piece of clear packing tape over it, make sure it goes on smooth. Let it cure up.
Remove the tape, it should look pretty dang good now, then dab on resin you've mixed up with your toothpick again, and cover that up with your tape. Let it cure.
Wet sand and polish to finish up. You should be quite impressed with the results.
Marble Falls/Seadrift TX