This thorough article by Manon Leclerc covers lightfastness standards, manufacturer classifications, and how to do your own tests for artist grade colored pencils.
Why do your own tests? Because sometimes it’s not clear which technical standards manufacturers use, how much their ratings differ from other brands, and depending on the type of pencils the available information may not be clear. Case in point: watercolor pencils. Often, you can’t tell if the information applies to the dry or diluted state of the pencil.
Some manufacturers like Caran d’Ache thoughtfully indicate resistance to light right on their pencils, Lyra puts it in a slip inside their pencil boxes, so if you are married to one of those brands and don’t use any others, choosing your pencils by those marks is all you have to do to insure that your work will stay vibrant for decades to come. That is, until you run into a situation where you really want to use this particular color, but its resistance to light is so low that you have to look at other manufacturers for something similar and more durable.
The next best thing a manufacturer can do after marking their pencils is to put lightfastness information into one document.
Manon did a wonderful job researching documents related to lightfastness of Derwent, Prismacolor, and seven other brands of colored pencils, gathering results in one article, and posting links for each brand.
Derwent makes charts for all their lines easy to find. The article mentiones some of them but the links changed since the article was published, so here are updated ones: Artists, Studio, Coloursoft, Drawing, Graphitint, Aquatone, Inktense, Watercolour. The full list of documents for pencils and blocks can be found here: http://www.pencils.co.uk/search.aspx?s=lightfastness.
My dear Prismacolor only makes this information readily available for Premier Watercolor Colored Pencils, Premier Soft Core Colored Pencils and Premier Art Stix, and Premier Verithin Colored Pencils. Their web site does not offer search, and I lack time and determination to hunt down the rest of their lines. Some day. Maybe.
Referencing the charts is a little more of leg work but still convenient. These two brands are the ones I use the most, so links to their charts go here as much for my own convenience as to benefit another fellow artist.
Still, nothing beats your own testing that allows you to see real results, not some printed or online images. Manor guides you through such testing and discusses the results that can be quite surprising.