[munificent]

Even that doesn't fully specify the problem since we don't know the prior probability of a random car being blue. Reword the question to be "rainbow", "chartreuse" or some other less common car color and the probability should go down.

[lisper]

> we don't know the prior probability of a random car being blue

That's true, but irrelevant. The problem stipulated that this car is in fact blue, so the prior in its being blue is 1.

[munificent]

The person being asked what the probability is doesn't know the fact, so the prior probability from their perspective isn't 1.