Car rental companies buy many cars from surplus dealer inventories, often towards the end of a model year. That's where they can get new reliable cars in bulk, and they don't care about color or particular models. So when you get an orange Aztek at the rental counter, that's because nobody bought it on the lot and Hertz scooped it up cheap.

I've been given an orange Dodge Nitro before. Most of the cars I've been given have been white, so much so I call the color "rental car white" and is the only color I exclude when looking for cars to purchase.

But yes, we can choose the category. And you will get it unless they are out of cars for that category. An orange Dodge Nitro was considered an "upgrade" from what I reserved. One time though I had reserved a Camry and they were out so they upgraded me to a Prius instead. It was nice driving the car back to the airport after a week of driving and not having to fill up the gas tank all week.

Sure you can choose your category. There's just no relying on it coming true when you arrive at the counter.

them-> "Here are the keys to your Dodge Durango"

you-> "no, actually I reserved a 4-door sedan"

them-> "I know sir but we don't have any left"

you-> "huh? I reserved one. what does a reservation mean?"

them-> "it's subject to availability sir"

In other words, (like many restaurants, like many airlines, hotels, etc), you can "reserve" anything you like, it doesn't mean it has been set aside for you.

welcome to the nuthouse

You didn't reserve a car, you reserved a rate along with a minimum standard of car, for some ordering of cars as determined by the company.