All Micarta falls into two catagories, UV stabilized and non UV stabilized. Most older Micarta will age when exposed to a UV source like the sun or a UV light. I have "aged" or yellowed white line Micarta grip panels by placing it under a garden variety black light for two weeks. I would check it regularly as intensity of bulbs vary.
UV stabilized Micarta is impervious to oil, stains, and pigments and will not yellow or change in exposure to UV. What you see is what you get.