OK... I am going to assume that when you refer to colored pencils you are talking about using them to color your edge-seams to match the printed parts. This is a good technique.
But if you want to use them to color your model, bad idea ( Like
@zathros said )!
Most of the weathering techniques out there are for plastic/resin models that have been painted first then weathered. In card, you have to ADAPT them to fit the material.
I would advise anyone to first seal the printed sheets before you even start the model, using a matte acrylic from a spray can something like Crystal Clear Matte Acrylic Laquer. Spray BOTH sides with enough that the sheet starts to become TRANSLUCENT, NOT RUNNY! Doesn't take much and will give a nice primed surface and help to resist water base paints from soaking in and warping the sheets. It will also allow you to WORK what-ever material you are weathering with or technique used... say for instance a wash to add depth and to bring out details... you need time to apply the wash and WIPE off where it isn't needed if the sheet isn't sealed it will just soak in.
If it is a white and black model ( no color ), washes are your best bet. Scribe over lines and greebles, then a VERY THIN wash of black to darken recessed areas ( scribed lines ), or used colored washes to paint over white areas. Wash should be barely visible when first applied and layer it till you get the effect you want ( you'd be surprised how the most diluted wash will stand out on pure white)!
Holler if you need help... it's a bit difficult without something to look at...