I keep a wool and a synthetic fleece blanket in the truck at all times. For out of town winter travel, a sleeping bag rated to -10C is added.

As for color, to me it makes no real difference as the blankets and bags would most likely only be used in the truck interior. It would be easier to carry a large orange plastic contractors bag if you ever needed something for maximum exterior visibility.
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Earth and sky, woods and fields, lakes and rivers, the mountain and the sea, are excellent schoolmasters, and teach some of us more than we can ever learn from books.

John Lubbock