Newspaper substrate coloring

[Iwantabeardie]

I want to put some newspaper substrate in my beardie's tank but I don't want it to be a dull grayish white. I want to dye it brown with something natural just in case the beardie accidentally eats it. I think coffee is bad for them so what other ideas? Should I just mix food coloring or is that poisonous? Thanks

 

[Iwantabeardie]

I want to make tunnels and stuff like that. I also don't want to buy anything because it already costs a lot.