Using white outlines

My Draw to adopt entry on deviantart run by .Metterschlingel.
I used a white outline, and this can look really cool sometimes.

Using black outlines can get boring.
Using different coloured outlines however, can make things look THAT much more awesome, and in my opinion, makes your work look more pro. :)

Do not however, pick a colour that just doesn't suit your colour scheme because this can make your work look a lot worse.