Many people don't fully understand these to very important terminologies that art supply companies use. "Permanent" means that the product will not move once it is on a porous surface when thoroughly dry. See that: porous surface. This fine printing on this definition is that some of these products when exposed to water on a non-porous surface will just lift off or when exposed to light will just fade away. (waterproof is different yet again.) Get this difference? It is kind of simple but scary when you invest in your art budget or make valuable room for supplies in your luggage.
Light fast means that when the product is exposed to light, depending on the pigments used, will resist fading when exposed to "indirect" light. The few responsible companies who test for this know that some dyes and pigments will resist or not resist fading and use 1 of 2 scales to tell you the results. These scales are regulated and controlled. Some pigments will just fade away and some seem to just fight back. For me, as an artist who sells my work and want to have a good solid product for my clients, I take light fastness seriously and it affects what I buy and what I use.
For my personal art, like journalling or maquettes for future paintings, I will use the lesser quality, lesser light fast products but NEVER for sale.
I was recently disappointed from 2 products, and they were gel pens and a "Derwent" product called "Inktense". I knew that the gel pen was not light fast but I did not realize that some gel pens are light fast to 2 weeks, inside my journal not exposed to light at all with a complete fade, leaving only pen impressions in the paper...I had to repaint over some art I made.
Normally, I expect and get and love the good quality out of "Derwent" but I did not read the fine print on "Inktense". These are said to be water soluble ink in either pencil or block that when dry are "permanent" and this is true to a degree. This is also an expensive investment. It is not however, light fast. This is where I got caught. This product is truly beautiful, versatile, fun and intense in color but not light fast. Disappointing, but also my own fault for not looking for the detail information. Not anywhere on product information did it refer to light fast.
None of the original art created from those products will go for sale as I take my art for sale seriously and responsibly, I can however make prints of the "Inktense" art pieces and have those for sale.
The last product that I want to talk about is copic or alcohol markers.... Folks these markers are beautiful, colorful, blend able, expensive and so NOT light fast. A caution or red light to be aware of is tints or dyes, these are usually unstable in light. So when purchasing these products, it is not necessarily a good one to use when you wish to sell the original, Sorry.
For the pleasure of using markers, I personally use Windsor and Newton watercolor markers, as they are light fast and proudly say that as these markers were thoroughly tested, and also Letraset aqua markers (now owned by Windsor and Newton). (no they do not sponsor me! It is what I have in my studio and my experience talking) These are not alcohol markers but I like the option of working them as a marker and also watercolors. They are more flexible for my needs. (You can also convert old markers into more light fast if you reload them with your preferred pigments, but that will be another article.) W&N do have an alcohol marker line but you have to look up their light fast quality.
To sum everything up, just because a product is expensive does not mean it is permanent, water proof, light fast or easy to use. Please consider this when you travel or move. Most of the really good artist (light fast) quality pigments are best to buy and bring with you, as they can be hard world wide. Know the details of your products. Look for light fast when you make purchases if you want those products to last through the ages, if not use whatever you like. Since I live in Ecuador, where the light quality is so strong intense that it will happily eat through many products, I search for light fast. I have literally seen projects disappear and fade within days.
This article is to help you purchase and purchase wisely especially if you move or travel to places where you need to consider these factors. This is one place to invest your art dollars, in pigments, paints and products that are worthy of it. Here is an information blog from Jerry's Artarama that helps to explain these things too. https://www.youtube.com/watch?v=1EBMFH9_pPE
(this art is 5x7 cart on bristol board, with Kor-i-noor polychromos colored pencil.)