There are a number of conversion kits that will allow you to change the color of your iPhone 4 faceplate to a variety of colors. They will void your warranty if you use them though as they are not considered to be of the same great quality that the original iPhone faceplates are made with. It’s always best to check Apple’s Warranty policy before you make any types of changes to your iPhone 4 or other Apple device.
To add color to your iPhone 4, your best bet is to choose a cover that has your favorite colors and designs on it and leave the faceplate alone. There are hundreds of iPhone covers you can choose from through online stores or even mall kiosks, so you can have a huge collection of covers and easily change them whenever you want without voiding your warranty.