There are a lot of options you can choose from. The most popular option for colouring in adult colour books is the colour markers. Markers are available in different colours and thicknesses. They are easy to use, and it is possible to draw fine lines using them without any training. You can also wear colour pencils. One benefit of using colour pencils is that you can erase the colours to a certain extent. If you want to create different shades, the best option is to use watercolours. It is possible to create a lot of shades by mixing watercolours. However, to use watercolours, the pages should be thicker than normal.