Seems like there was another thread on this a while back. I recall the need for washing the mats. These mats are one of our most necessary pieces of equipment. So far I have only replaced one -- then learned that you can extend their life a bit if you:
1. Don't cut on the very same line every time. Move over 10 inches if you have to repeat the same width cut a lot.
2. Keep them out of the sun unless they have somehow warped and you are using the heat to try to flatten them. If they have been stored and somehow warp a bit, a warm soak and laying them flat will probably correct the warping.
3. A damp microfiber rag will clean fibers out of cracks quickly and cheaply.
4. The mats do like moisture. If they are too large to soak, the damp microfiber rag treatments works well. Just leave the rag on it overnight when you're sleeping and not quilting.
I have a 58" long mat that has been in service for 4 years and still looks and works fine.
5. White mats are not any more of a problem than any other color. The biggest problem I've found is the thickness of the cheaper mats. The small thin mats I've used don't seem as durable.
6. With continuous cutting in the same area, any mat is going to show wear, whether it's indentations or fading of the gridmarks. My personal opinion is get as large a mat as you can utilize. You have more room to move to various areas of the mat to use to cut on. A small less expensive mat can be put on it for squaring block as well as rotating for trimming those awkward areas. So far I haven't had to purchase a rotating mat, just used my small mats that I take to class.
7. If you have a "bad" mat, it can be recycled. You can cut it up (depending on its original size), & use it for a sewing machine mat, a small mat to square blocks, the bottoms in totes and bags, a small piece is a great place to put your coffee cup so the heat doesn't affect the mat you're working on. Imagine there are tons of other uses for has-been mats. But that can be another thread.