A: The Touch Up paint would be the color of the Main Product. i.e. Brunswick Brown, Himalayan Brown, Tuscan Brown. In any of these Paint Kits, there is a Bottle marked Trim. This is the Color you would use to touch up the Cap.
A: Matching Cap would be: NextStone Slatestone Post Cover Cap Brown 10.5 x 10.5
A: The caps will have to be cut in half then the opening for the post to continue through would have to be jigged out. Here is a video showing exactly that: https://youtu.be/uK3sqsj6o2U