Lets start this learning session with a tell all picture...
(This is a picture from phenixflooring.com)
If you see how the material is dyed when it is introduced to lets just say... bleach it won't change the color of the carpet. I however don't suggest putting bleach on your carpet because it can eat the backing, but it does let you know that it can be cleaned.
A few Q & A that I have answered over the years that I feel that I should share.
Q: Is it un-stainable?
A: No, it isn't. It is close, but there are things that you can spill on your flooring that can still create a stain.
Q: Is it easier to clean?
A: No, but the stains will come out a little better if you are working at them.
Q: Is this fiber effects by the sun?
A: Yes, all carpet is effected by the sun. It can be affected by sun rot or sun bleaching ( I assume) I haven't had anything that I have found otherwise that tells me I am wrong.
Solution dyed is a great option BUT it is not the only option. There are so many different great fibers and fiber protectants like R2X, Stainmaster, Lotus and many other protectants that give your carpet a 'lifetime guarantee on stains' that I still love and would install into my own home. I do however like to give some education on carpet fiber and dying styles so that you are able to have a little extra knowledge as you shop around for your carpet.
What does this mean (to me)...
There are so many different carpets to choose from and now days. I like that carpet is more cleanable than ever (this does not mean it is non stainable). I think you should pick carpet on how it looks and where you are wanting it to preform. Make sure to ask questions, we like being able to help you look and choose what will suit you best.