Changing the colours of lines

Hey guys
I wander if you could advice me. I'm creating illustrations using colour pencils, then I scan and play with colour reversing. However I am not completely happy with the fact that black contours after reversing colours, change into white. I would like to be able to change the white into something else, for example yellow, and to do it with one action for the whole drawing. That's one thing.
After being able to change white into something else, I was wandering if instead of using plain colour to replace white, I could use textured colours.
Here is a link to my works, have a look and tell me what you think, please. http://kalpek.deviantart.com/gallery/
Really appreciate!! Cheers

 

One way to change all of one color in an image, use image / adjustments / replace color. Select the color(s) you want to replace, adjust the fuzzyness as appropriate, and then use the HSL sliders to change the colors.

An alternative is to use "select color range", to select all of the color you want to change, then you can use any of the adjustment tools to change it, or Fill that selection with a new color etc.

To replace white with a texture, one method would be to add the texture as a Layer, duplicate the Background as a layer on top of that, then use the blending layer options to not show the white parts, which will then reveal the texture where it was white.

Hope that helps !

Chris