Final answer:
The color of John's car is not specified in the question as details provided are not relevant to determining the color of the car.
Step-by-step explanation:
The question "What color is John's car when it's not invisible during the weekend?" does not have sufficient information provided for a definitive answer. Information about the cat's color on different days of the week or the number of apples John has does not logically relate to the color of John's car. Therefore, the correct answer is C) It's not specified.