How well can humans detect vitamin-richness?
Based on what I could search I guess that humans (and other organisms) usually do not have strong sensory mechanisms for micronutrients (Miyamoto et al, 2013). 

There are some reports on sensing of metal ions, especially zinc and copper, by some organisms, including mammals (Bird, 2015; Ballou and Wilson, 2016). However, I haven't come across any study that talks about vitamin sensing.