It is not easy to gauge how a user feels when interacting with a product. But if we can somehow know, learn and understand this, it can help us optimize the user experience. Currently, research in this area is focused on gaining user insight directly from the user. But users are not always objective in their answers and often fall prey to their biases. Many times, we find that the participants knows what the researcher wants to hear and they report their emotions accordingly. Sometimes, they cannot even interpret their own emotions.
About one in every 12 men, and one in 200 women are affected by color blindness globally. As a UX designer you would want to make sure that your webpage or the UI has a color scheme considers individuals with colorblindness as well.