After asking "Why didn't food coloring dye my [acrylic] yarn?", the most frequent questions I get are about whether yarn dyed with food coloring is colorfast and lightfast. Today I wanted to address the lightfast question.
The simple answer is that no, food coloring dyes aren't light fast. If you leave yarn dyed with food coloring in direct sunlight for months on end, you will see some fading. In the following video, I show an amigurumi butterfly that I knit (the wings) out of yarn dyed with food coloring. I left this butterfly on my windowsill for months as decoration. I realized one day that the colors on the wings have faded a lot, especially when you compare them to the yarn on the underside.
In contrast to the butterfly, some winter accessories that I knit with the first 100% wool I ever dyed have very little fading at all. I wear these accessories frequently in the winter (which involves going outside in sunlight) and there is no apparent fading. When I get home I frequently toss these on a chair, so they're exposed to light constantly... just not direct sunlight.
It isn't just food coloring based dyes that aren't lightfast, you can see fading on many different objects, too. I think it is a good rule of thumb to keep things you don't want to fade out of direct sunlight.
Check out the following video for more of my explanation.
There is another hand dyed item that I didn't share in this video... my 10 hour afghan. Since this blanket normally lives on a chair in my living room it has been exposed to light for years. I have no idea how much it has faded, but there is still a lot of color in the blanket (knit with a mixture of commercial and hand dyed 80% wool/20% nylon yarn.)
I create a new playlist for the videos I make based on FAQ's. I really hope these help! Please let me know if there is anything else you wish I'd address on my channel.