fountain pen on brown paper

I recently bought a fountain pen, for traveling, rather than the dip pen, the nib is a bit inflexible, but otherwise now that it’s worn in, it is pretty nice to use, along with brown paper, taking down the contrast of my images, I do need to work on my focus point though, and unfortunately the iPad is terrible at matching the colours’ so we’re loosing the lovely brown of the paper, but I’d prefer to focus on creating than trying to individually match the colour of all these, if anyone knows of a an app that can batch recolour please let me know