Do you know why denim jeans have the color in our colorful cursor pack? Blue was the chosen color for denim because of the chemical properties of blue dye. Most dyes will permeate fabric in hot temperatures, making the color stick. The vast majority of jeans are dyed with synthetically produced indigo, which imitates the color of the dye extracted from the Indigofera plant. Denim is available in many colors, but the most common is indigo denim, in which the warp thread is dyed while the weft thread is left white.