One of the most exciting traits of succulents is their ability to change colors. They can change colors in response to environmental stress such as bright sun, drought, or cold temperatures. Some genera, like Sempervivum (Hens & Chicks), even change colors regularly through the seasons.
In general, you can expect the brightest colors in spring and summer. Not all Sempervivum change color so dramatically; if you want more consistent year-round color, check out Sempervivum heuffelii.
If you notice colors fading to pale, green tones along with a stretching of the stem, it is likely that your plant is in need of more light. Try moving it into a sunnier location or under a dedicated grow light and watch to see if the color recovers. For more information, check out the full guide to Using Sunlight to get Colorful Succulents.