How do you create a hand colored effect, like in the image above, using either Adobe Illustrator or Photoshop? I'd like to know how they colored the arrows and how to add a rough gradient like the one on the blue box.
It does look like scanned and manipulated art. The folders are obviously a dupe, but possibly was conceived as a stand-alone icon and then duplicated. A lot of the brush work looks responsive, which makes me wonder a little about whether it was automatically generated or not.
However, in Photoshop, you can simulate colored pencil using brush dynamics (window>brushes).
Your taste will differ from mine, but I made a preset by selecting one of the "smear" or "splotch" default brushes, and enabling "Scattering" with "Scatter" at 233% on "Both Axes" and a "count" of 7. I then set the brush "flow" to 10%.
I made a layer with a regular brush to draw the outline of a box, and then a layer below that using my brush preset for the shading effects. I painted it using black, and turned on the "color overlay" layer effect.
Note that I drew this with my mouse, so artistic critiques will be met with extreme lugubriosity.
You can always look for Photoshop/illustrator brushes but its probably just handmade. If you are going for a hand colored effect, why not hand color it (and then scan it)?