I wrote the samples in the image below on a page of Rhodia 80 g/m2 5 mm grid white paper using a Pelikan M400 14K fine point nib. (The original photo is 3.9 Mb so I had to save it as a TIFF file to get it below the 1.95 Mb limit - no noticeable loss of color or detail.) I cut the page vertically and kept the left half in a notebook, and placed the right half in the sun for approximately 50 hours. The inks used in their order of appearance in the sample writing were: J. Herbin Bleu Pervenche; Pelikan Royal Blue; Levenger Cobalt Blue; J. Herbin Bleu Azur; and J. Herbin Café des Îles.
Some observations I thought you might find useful:
The Pelikan Royal Blue ink faded the most, and the Levenger Cobalt Blue seemed entirely unaffected. The J. Herbin Bleu Azur was second most affected and the J. Herbin Café des Îles was second least affected. I was surprised at how the Pelikan Royal Blue faded almost into invisibility, and was not surprised about the J. Herbin Bleu Azur being strongly affected by light. I was very pleased that my favorite inks, the J. Herbin Café des Îles and the J. Herbin Bleu Pervenche were nearly unaffected and can therefore be expected to last indefinitely under normal document storage conditions. I wonder if the Pelikan Royal Blue is more susceptible to fading from other environmental conditions as badly as it is under bright light?