So I see these amazing artworks, and also Sylesti's in general.


When you do the drawing (digital/paper) how do you color the drawing without coloring over the details, will you have to re-draw the details?

For digital I use layers.
For paper, I use pencil first and then outline it in sharpie or pen

But how would you remember how the little details look, and what are layers?

Because I make sure I can still see the pencil lines

I mean for digital

Layers

You have to redraw the details, I use lots of layers

layers are something you can use in art programs like the Adobe programs and Sai (not in MSPaint, though, it doesn't have them), and they are exactly as the name suggests, layers.
So on layer one you can draw something out, make a new layer, go over those lines more clearly while keeping the sketch untouched, then make said sketch layer invisible or lower opacity, make a new layer and use it to do the base colour etc.
We ourself are one of the people that tends towards Lots and Lots of Layers
Here's just the wing section of our summer avatar contest entry:

Mosly because it hits the top and bottom of the screen with just that... >`->;
Most of the layers there are in groups (/folders), and are set to invisible because I keep previous versions and make layer copies when I'm about to do a new bit- only the stuff between 'touchup2' and 'layer 101...' are visible.
Doing this we can always go back and check previous stuff.

Lots and Lots of Layers
An Unrelated-to-Sylestia example of layers
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2
3
4
5
(and you might notice that the file name has 'layerclear'- these are the refined versions, a save where we deleted all the previous attempts, sketch layers etc. for sake of file size and loading time)
Here's the multiple sketch layers in the original file in their assorted levels of opacity and colour.