The color to fill the words in "What Color to Fill the Words" should be determined by the context and the intended emotional response. Based on color psychology, blue is often recommended for its calming and soothing properties. A study by the University of British Columbia found that participants who worked in a blue-colored room were more likely to be creative and less stressed compared to those in red or green rooms. This makes blue an ideal choice for a text that aims to evoke a sense of calm and encourage thoughtful consideration. Additionally, blue is known to enhance focus and productivity, which could be beneficial for a text that requires deep engagement.