That is age and sun damage. The fix is to spray ALL of the interior plastic with spray dye. If you only do some parts they will like new and the others will look old so to make it all look good you must do it all. The key to a good job is to really get the plastic clean before you spray it. You must remove all traces of any goop that was used like Amor-All or anything silicone based. The best job is done by taking every piece out of the car and spraying them all together on a dry windless day out of the sun. One "trick" I used was to hold the spray can farther away then you would typically do, it allows the spray to dry just a bit and leaves you a more textured surface. Smoke grey is the color but a lot of auto stores can color match and make up cans for you. You also use prep spray to improve adhesion before spraying the vinyl dye (this isn't spray paint).