This is so disappointing, i am sure you didn't choose a good quality lipstick cause i've used different branded lipstick but never got changing color problem, but the fading problem is quite obvious. Do you get such problem with every lipstick you use?
In all the branded lipstick i used, i have a preference for Maybelline Lip Smooth LIpstick, it's the best.

Of course they will fade with time. In fact they don’t fade but unknowingly you brush against it and they are rubbed off.
So, avoid that and constantly keep on re-touching your lipstick.

It also depends on type and brand of lipstick you are using, normally you should use your lip liner as a base for your lipatick, this will ensure that your lipsticks last longer than usual!

I think it depends on the lip color. If your lips are dark then whatever lipstick you’ll wear will appear dark shaded. One lighter colored lip, the color of the lipstick appears as the color in the tube appears.

I have noticed that dark color lipsticks last more longer than light pale color lipstick, yes, i would say it all depends the color!

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I have notice it too; the color fades with time. Whenever I see my lipstick is loosing its color then I apply transparent lip gloss over the lipsticks; the color of my lipstick is enlivened instantly. Otherwise I don’t any other means to stop the fading of the lipstick color.

At night the lips tick never changes color but during the day it does. This is so because of the sun; it affects the lips and causes it to darken so the lipstick appears to have change color. It is in fact the lips that have changed color.

I don’t know. But this is not a problem. If the color is fading then new lipstick can be applied afresh. There is no need to worry about it. Nothing is permanent. I would have never liked that my lipstick is permanent.

Do you think the lipstick is reactive to the elements in the environment and makes it lose its color? This is true that the color changes. I don’t know how to save the color; I use to reapply the lipstick.