Here's a Copic tutorial on how I colored this bouquet (click on any photo to view it larger):
These Copic Sketch markers were used for the entire bouquet:
If you don't know about these markers already, what you first need to understand is the numbering system. The first letters represent a color family: YG is for yellow-green, G for green, R for red, E for earths and so on. The last digit of the numbering system is the lightness/darkness within that color family -- this is the reason R81 is a light pink within the red spectrum and R08 is a darker red within the red family. The middle digit is the color tone or brightness/dullness, so R08 is actually on the lighter, more orange end of the red spectrum, while something like R59 is on the other end of the red spectrum, containing more red/violet tint.
To achieve the variegated roses, I used the lighter red/rose Copic marker R81-Rose Pink to lift off some color from a darker red R08-Vermilion:
Then when you first touch the lighter marker to paper, you'll have the darker red color fading into the lighter color. You can see this shading technique a little better in the straight squiggled line . . . the swirl is how I actually colored the roses, starting in the centers where color is usually darker on a rose.
With these alcohol-based markers, you don't have any fear of ruining your lighter marker, because as you can see, the more you color & scribble with the marker, the darker color is removed from the lighter marker.
The wrapper around the bouquet was colored much in the same way at the top, and then adding the #0-Colorless Blender pen towards the bottom of the wrapper and using it to lift off some of the lighter R81 Rose Pink color and fading it into almost white, to leave a lighter color of highlight.
The leaves were colored a little differently. I started by using the lighter green YG03 and colored the top halves of the leaves, since these would be naturally lighter, with a light source coming from the top:
Then I used a darker green G24 to color the bottom halves of the leaves:
Since the green colors ending in 3 and 4 are so close within the green color family, you'll achieve a subtle but noticeable difference in the shading.
The shadow you see around the right side of the bouquet uses C-1 (C stands for the Cool spectrum) to give a light, natural shadow and make the bouquet appear more three-dimensional:
I hope these tips have been helpful and I'll certainly have more of them for you in the future!
Edited to Add: I've had some questions as to the ink and paper I used here . . . my apologies for not mentioning those (you all usually keep me on my toes!). My favorite non-smearing ink to use with the Copic markers is Brilliance Graphite Black or Pearlescent Chocolate by Tsukineko. Once you stamp your image, let it air dry thoroughly, or if you are the impatient type like me, zap it with your heat tool for a few seconds to dry it quicker!
My favorite cardstock to use for any kind of coloring (watercolor, dye-based inks or watercolor crayons) has been a shimmery white for several years now. Stampin' Up's Shimmer White is the same (in my opinion) as Arjo Wiggins Curious Iridescent Cryogen White (available from CutCardStock.com). This manufacturer also makes a beautiful vanilla shimmer cardstock (Poison Ivory) you'll find in the highlighted link above. It is also available at PaperZone storefronts, if you happen to have one near you. I'm happy to report this coated shimmer cardstock works GREAT with the Copics and is just about the only thing I use for coloring stamped images!