The fraction of colors that are purple in 20 trays is 5/20, or 1/4. This is because each tray has 5 colors, and there are 20 trays. Therefore, the total number of colors is 5 x 20 = 100. Since one of those colors is purple, there are 100/1 = 100 purple colors. Thus, the fraction of colors that are purple is 100/100 = 5/20, or 1/4.