Blending of colored pencil is done by building up layers of colors one over the other and using the multiple colors to burnish over top of each other.
I used 4 colored pencils: White, Black, Medium Violet, Dark Purple.
Define the light source as being above the ribbon.
Use medium Violet to lightly shade the top side of the ribbon (the side, that faces the light source).
Use Dark Purple for the areas that do not receive the direct light. 
Shade with Medium Violet the sides of the curves. 
Use White pencil to blend the highlighted areas. 
Use Black to add shadows to the darkest areas.
Use Dark Purple for blending.
Color in a curved surface:
I used 3 pencils: White, Medium Green, and Dark Green.
Start with a Medium Green.
Shade lightly most of the surface.
Go over with the same Medium Green pencil and color more, leaving the middle as is. 
Use Dark Green and color in the sides of the shape, use Medium Green again to blend the two colors. 
Use White pencil to blend the middle part – the lightest area.
Use color blending and burnishing techniques to create a 3D ribbon
You can make any kind of art with colored pencils!
