Indeed, that is the basic issue @Sirtel, @rcentros. For regular reading, colour is not needed because its use is very limited (underlining, links, covers, some images, titles and little else. On Android it is also useful for external applications that are usually used for dictionary, translation, Wikipedia and book organisation). Its usefulness increases for the more or less specialised reading that you have mentioned. And this is where the question arises as to whether current colour technology is valid. My impression is that the new screens have (pleasantly) surprised the sceptics. The reviews point in that direction. And I agree with this assessment. I believe that, even with their current limitations, they are a major departure from the previous generation and can be used with a certain degree of satisfaction by those who need them.
(Speaking of the Tab Mini C, I think the most balanced review, summarising its advantages and disadvantages, is the one posted by Chalid Raqami on his YouTube channel:
https://youtu.be/EAyNoLYrxBk ).