I am currently colouring some line art in Photoshop. The line art is black and white, so I have set the layer to Multiply and put it on top of the other layers. My problem is that the black remains somewhat transparent, and you can see colours underneath. Is there any way to do this and make the black completely opaque? Any help would be appreciated!
The black is probably still slightly transparent because it needs more strength. Try boosting the strength of the black (levels, channel mix etc.) and see how this works. Just keep an eye on your ink limit to see that it stays within your specifications.
If your still not happy with the representation, what I usually do with line art in this circumstance is: