i was studding linguistics and something got me thinking. it seems that i couldn't find answer anywhere so maybe this question is stupid

so for example: we want to connect two concepts. "car" and "blue". so we connect: "car is blue"

my question is about next time we want to connect those concepts. they will be already connected so we say: "blue car". but we dont talk like that without verb

so why do we need to say "car is blue" instead of "blue car"?