The key to a nicely colored image - just like a layout - is depth. Laying down a single color is nice but somehow seems incomplete, no different than adhering a photo directly on a big sheet of paper with nothing else, and then calling yourself done. So, before we begin, make yourself a shadow guide. I've used the insert from one of my embellishment packs for mine - a simple sharpie does the trick (though you have to go over the lines a few times to get it dark enough)
When you have stamped your image (I've used versafine with clear embossing powder on georgia pacific paper), the guide will visually guide you as to where the shadow should go, depending on WHERE the sun is behind your image. Here, I'm working with the tree from the Eco Chic set from Unity Stamp Company, and I've laid the shadow guide over it - the end of each line is the end of where your sun ray would have gone, and therefore, where your shadow should be the darkest.
Here, at high noon, the sun is directly over my tree, and the shadow would be directly beneath it.
Contrast that with here - sun is in early afternoon, and shadow would now be to the bottom left
Getting started, just color your image like normal, with your lightest color, holding your pen upright and moving in small circular motions. If you are using the brush tip, remember it is flexible, so practice a bit on a scrap piece of paper til you get the feel of the motion vs. color transfer, then color away.... It doesn't have to be perfect - but do cover all blank spaces.
Next, lay your shadow guide and get an idea of where your shadow needs to go.
Now, take your medium color, and color your shadow approx. 1/3 of your image inwards...
Next, take your third and darkest color, and apply a thinner line at the edges of your shadow
See the transition lines where your markers meet? Yuck. Now, here's the magic of the Copic. Take your lightest color again, and go over the darker areas and the lines, again in small circular motions, and watch those ugly lines blend away. It is important here - be patient, and keep your pen upright with only a slight angle, and circle circle circle with your pen tip... (please ignore the stray line - its hard to take a picture with your left hand when the right hand is coloring)
When you're done, those lines have disappeared. A note here. By the time you've reached this blending step, your lightest color has dried. When you go over it again to blend in your darker areas, you will see that when the light marker goes over the dried part of that same color, it is now noticeably darker - by about 1/2 a color value. SOOOO, to keep it all fairly smooth, eyeball it and apply as much as that lighter color over the prior colored areas to ensure a uniform color.
You use a lot of color in this process - if you've done it right, it has saturated your paper, and the backside looks somewhat like this. It will take some practice before you find the right level of saturation for you. For me, in my dry climate - if I do too much saturation, my colors can bleed, so you can see that my top branches (where there is less shadow) uses quite a bit less ink than the bottom part.
Now, for the leaves. SAME technique, but now, since my surface area is much smaller, use your markers with a much lighter touch so as to stay within the lines - there is not a lot of surface for circle circle circle on the leaves. There is no magic as to how - you'll get the feel for it. Here we are, lightest color first. Pretty - but flat:
Shadow guide to remind myself where to place the shadows:
Medium color about 1/3 way in:
Darkest color at the edges
After blending with the lightest color: Here, the first time I blended with the first color, it seemed to blend too much of the shadow away - so I repeated the steps with the medium and the darkest color, and blended a second time.
(Just a followup on my note above regarding pen angles and bleeding - it is possible to oversaturate, and the ink can bleed, esp. if your pen angle is too slanted and its kind of pushing the ink ahead of it. Practice, and you'll get the hang of what works for you.
And because I messed up with that hand slippage due to camera incompetence, I cut my image out, and here is my card:
