Sorry to hear that the Texas sun is taking its toll on your bag. I think a red fabric pen sounds like a good idea. Luckily it's just the trim on that bag. The all red stand bags are one of the hardest colors to keep true. They tend to fade to pink and the all white bags tend to yellow over time. I have the white Cart 14 on my EZGO out here in AZ and I know a couple of summer will be all she can take. Scotch Guard will likely help as there is also several products designed to protect outdoor furniture from fading. Do a google search for brands and prices.

I have for years advised, based on personal experiences, if you live in any southern/lower of the 50 states not to purchase any bag that has red on it. It will fade after about a year, maybe sooner, due to the hot sun. Texas is like our weather here in S Carolina and the red will eventually turn pink over many years. What do I recommend? Nothing, other than purchasing an all black bag. Red is not a good color on any product in this type of heat. I always buy an all black bag with no red trim. Lesson learned over the years. This happens, regardless of the brand or product.
We purchased a red Volvo around 2000. They did not put clear coat on them that year in red, white and black.
Wife had to have it. Totally faded out, on the hood, top and trunk. Nothing is sacred in out weather. Lesson learned.

I have had this happen over the years on a few bags that are used in intense sun like AZ, TX and FL. It is just the sun exposure fading colors as it does with other items. I try to keep a towel over my bag in between shots to minimize this fading. Some have used a spray (cant remember but I think it was a water proofing spray) to minimize this problem.

I know Titleist has been working on this over the years and experimenting with different materials.