Vivid Coloring

I've been recently trying to perfect a coloring action and I was wondering how these icons were made:

I usually see these colorings in Veronica Mars icons,

starlingsby100:

teh_indy:

__lindy:

and the muted but still vibran-ty

inxsomniax:

Can anyone direct me to a tutorial for vibrant coloring like the first three and at least how the 4th one was made?