You can achieve an interesting combination with alcohol markers and gel pens when you first color thewhole image with markers and then, on top of that, color the details with gel pens.
The left side of the figure is made with the markers only, and the right side has been finished with gel pens.
Please note that the background color may change because of gel pens in an unexpected way. Sometimes the result might be a very marvelous shade. You should therefore try the colors on a different piece of paper first, if you do not want to be surprised.
With this technique, you can have a vivid, and to my opinion, also a more balanced outcome than you could with gel pens only.
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Pens: Alcohol markers (Promarker etc) and gel pens
Book: Mental Images vol 1