To keep your labels from yellowing and fading in the sun take a look at UV protection spray for your labels. For labels that are going to be exposed to the sun for extended periods of time, the addition of a UV spray can add an extra level of protection. For naturally durable labels check out our Waterproof Labels.
Most clear coat sprays are a lacquer based product so be sure you have a clean surface before coating with the clear coat spray otherwise you may see finger prints. Shake the can and hold about 4 to 6 inches from the labels. Apply an even coat but not so much where it's dripping. Once you use the spray give about 5-15 minutes for it to dry.