This is a sign of illness. Good comb color requires healthy blood flow. It could be a sign of many different conditions. Not knowing her age or anything about her, how she is acting, eating/drinking, pooping, condition/quality of her eggs, if she is at a good weight, been exposed to any potentially toxic things, is injured, what kind of diet, etc, I couldn't tell you specifically why this is happening.
If she were mine I would keep an eye on her. See if she seems to be getting worse or better during the day. You might need to think about separating her from the rest of the flock, if you have other chickens, in case it is something contagious.
With chickens, unless you can take them to a vet for full diagnostics, all you can do is treat symptoms. In this case I would make sure she neither gets too hot nor too cold. That she's not being bullied by other chickens if she is acting weak.
Often by the time a chicken is showing signs of weakness, they have been sick for a while. Most bird species have to act normal and will until they can't. By that time fast intervention and support is needed, if anything can be done.
Giving vitamins/electrolytes is always a good idea. These are supplements that are basic and can often help support a chicken and return them to good health if there is nothing more serious wrong.
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