Hi,
One hint.... if you look the printed image with lens, you'll see that the black is not good - it's more strong near the ends of the lines and it's more transparent in big areas. It's some electrostatic effect of disattraction the charged ink.
Some firms sell speciall sprays that make colours dark and dense - you just spray over the printed sheet and you get extreme dark and dense print.
I saw that some people use one other way, that gives better results.
Just put some disolver for nitro paints in flat plate. Put your image over the vapours for several minuts, until the colors become dense and dark enough. It's good to put the disolver for nitro paints into some closed box, to avoid evaporating and smells.
Best regards
Luben