How do I prevent pencil colour drawings from fading away while I'm still drawing it?
Building on @Joachim's comments above, yes, the direct sunlight can affect the color and make them dull. Hence, when you are not working, you should store the paper in dark
(or use some protective varnish)
Also, Do you wear any artist's glove while  (A glove that covers ring &amp; pinky finger)?
-&gt; If you are not using it, then it might help you with smudging and fading of colors.
-&gt; If you are using it, you might want to check the fabric and see if that's what affecting the pigments.
Also, placing some other paper to cover the already drawn part, when working on details might help.