There are endless possibilities for colour schemes. You can also combine different techniques to create an even more varied palette. This makes effects easier to perfect: mist, reflections, stars, smoke, or more abstract backgrounds in ink, for example, depending on their characteristics.
Tip: Some techniques are difficult to superimpose. Do some tests on a draft to see how the pencil reacts on the felt-tip pen, or the felt-tip pen on the pencil, for example.