Quote Originally Posted by impulse View Post
So is it like this?

Я хочу красней машины - I want a car with a specific color.
Я хочу машину - I want a car. More general
No, я хочу красной машины is not possible. That's not about its color, it's about the fact that you imply only one car so you can't really say that you want a part of a car. That'd sound ridiculous, wouldn't it? So Я хочу красную машину is the only correct usage.

However if you go with a plural you may use genitive because as I said many cars can be considered just as a part of something bigger. Like you want two cars out of those 5 cars. See the logic?

Я хочу красные машины and Я хочу красных машин are both possible

Cheers