Contrasting collar undersides, shirt plackets or cuff linings are one of those details that can make or break a shirt,designed through the shirt design software. For anything other than a casual shirt, they are not really suitable at all but at the end of the day it depends on your style. Use them wisely and they can elevate the shirt to a new standard, go overboard and you may end up looking clownish at best.
In my opinion, contrasts work best when used with subtlety and when not immediately visible, sitting in the background while the rest of the shirt shines, until it’s time for them to make a memorable appearance. Mind you, shirting contrasts are not only limited to fabrics: details such as buttons, buttonholes or threads, although in a much smaller scale, can have an enormous impact on the global aesthetic.
Personally, I try to keep fabric contrasts as simple as possible, sticking to the traditional alternatives such as a contrasting white collar or cuffs on a classic shirt or at most, a contrasting fabric on the inside of the cuff. Even though I’m not the biggest fan of contrasting elements on a shirt, some details such as a contrasting color on the ascolite thread or on selected buttonholes can make a world of a difference and become a personal trademark.