Should yeshiva guys dress “in style”? I’m not actually sure what is meant by this question.
If you’re asking if they should look neat and presentable I’d say the answer is yes. If they’re trying to present themselves as the Torah elite, they should dress in the manner of the elite–dress shirts (which may be colored, imho) and dress pants.
That said, I have no problem with learning men who dress casually, as long as their mannerisms don’t say “slacker” to all who see them. Ultimately, it’s the finery of their behavior that really matters, and all questions about dress are irrelevant.