I'm surprised it isn't mentioned in the article, but you can get rid of yellow stains by putting your clothes out in the sun.
They did test with UV light. The sun is broadband (it will have both blue light and uv light) so it works to a degree. The insight is that uv generates some new yellow coloured compounds and only using blue light prevents this.
For instance "color-bleach" (which I guess is peroxide with other stuff) makes cloths disintegrate if used too often
It's not true that if you expose tissues to lots of H₂O₂ they'll get cancer.
Washing clothes in a dilute peroxide solution is not going to cause cancer, therefore simply walking outside to hang your clothes carries substantially more cancer risk than the use of Hydrogen Peroxide.
Saying it causes cancer in “small amounts” is a bit like shouting at someone that stepping on a twig is destroying the entire forest…while standing next to an inferno.
I dont, but I dont care.
You're 100% right.
As long as the photon is energetic enough, it can cause a radical and therefore break a chemical bond.
Brighter the sunlight, more peroxides (or radicals) made, more damage to your skin or your cloth's fibers.
This is also why anti-oxidants are so effective at protecting the body, why inflammation is so damaging (body produces peroxides to eliminate what it believes is a threat), over consumption of food, too much/little exercise, etc. they all affect peroxide concentration or their halflife.
When you do it with actual flax linen it is quite stiff afterwards and it may form permanent creases if you treat it in certain ways immediately after, depending on the weave. But that's to some extent always true with linen.
When I lived overseas my laundry was often dried in the sun and it’s amazing how fast the color is bleached out.