Hi Aaron, No, we do not need to always follow a color with 色. However, not using 色 can (although not always) change how a phrase is composed. For instance, 白书 is a perfect way to say "white book," but if 色 is included, the particle 的 should be as well (白色的书). Here is an example: 我穿绿衣服。 我穿绿色的衣服。 Both of these mean "I wear green clothes," but with the removal of 色 in the first sentence, we also have the option to remove the particle 的. I hope this helps. Please let me know if you have any more questions =)

Both are grammarly correct，but 白的书 sounds not so natural 我想买一本白色的书。 it's better to add 色 when making an independent sentence 你想买哪本书？白的那本。in this case you don't have to say 色

汉语中，单音节对单音节，双音节对双音节。 比如，我们可以说“红色的衣服”，但不可以说红色的衣。

白的书 sounds extremely awkward. You should use either 白书 and 白色的书. You use "色" in 白色的书, not to emphasize that it is white-*colored*, but to make the expression more balanced and euphonious. The pace of the phrase is either 1-1 (白书) or 2-2 (白色的书). To add to Mr. Zhang's excellent comment, I would say it's not *always* necessary to add 的 after 色. There are expressions 绿色通道 (fast track, lit. "green passage) and 绿色蔬菜 (green [often in the sense of "organic"] vegetables) that require no 的.

“白” when it's used to signify a color, it has already contain the concept of "色"，hence here "色"is not necessary. But if you want to refer to a variegated thing, you need to say "杂色"。