First of all...gotta correct small glitch problems in those two sentences :D zhè liàng chì chē shì lán sè de. tā bú shì hóng sè de. You should say"qi che",not"chi che" Um...I think these two sentences are absolutely right. well...hong se lan se,if a color word without "的"(de),it can be usually considered as a noun...but when a de added to it...it can be regarded as an adjective. Of course,..you can leave out the word"色"（se4）,hong de红的 lan de蓝的

From the meaning, these two sentences are right. But I think the former is better. Just as nalan said, the subject ( tā ) of the two sentences refer to different things. The subject in the whole sentence should refer to the same thing.

tā bú shì hóng sè de--------it is not a red car. tā refer to (the car) tā bú shì hóng sè-----------the color of the car is not red. tā refer to (the color) both sentences are right.I guess you want to write qì chē not chì chē.

zhè liàng chì chē shì lán sè de. tā bú shì hóng sè de. zhè liàng chì chē shì lán sè de. tā bú shì hóng sè. Both sentences are right.If you speak with a Chinese,both they can understand. tā bú shì hóng sè de.---->the tā stands for the car (che ) tā bú shì hóng sè .------->the ta stands for the color(se)

Car..qi che...汽车...is a palatal sound,not retroflex...:)