Add two rectangle over the top. Color one brown color and set the opacity way down. Experiment with blending modes other than Normal. That'll do for the color.
In the other rectangle, use the filters to add noise. Play with the parameters on that. Play with the blending modes and opacity value on this layer.
Alternatively, try adding a stock image of some old paper over the top and setting the blending mode to multiply. I found some nifty distressed paper textures here: http://zentextures.com.
Thank you very much
a million thank you's
this was the perfect solution
for the win!Thank you very much you turned my crappy little fake comic book into a more realistic work. thank you
Realism is in the details, that's for sure.
You could also ditch your computer and fetch from your closet a comic book that's been around for 50 years or so...