The best waste is of course no waste, but as long as that is a utopia, there is nothing better than coming up with creative ideas with waste materials.
One of the most beautiful sayings I ever saw was: Waste is only waste if you waste it.
And once you get used to thinking in terms of reusing and not wasting stuff, a huge flow of ideas will start, I can assure you.
In this article, I list a number of ideas for inspiration or imitation.
Decorating your ceramics can be done in many ways. Your clay object can be glazed or painted with engobes and underglazes. Even screen printing or applying transfers are possibilities.
A pure way of working is using the colour of the clay itself with at most a transparent glaze to emphasize the colours and make the object watertight.
Clay has different colours depending on the substances in the soil of the quarry. The clay you buy in the shops usually has only a few colours: it’s white, red, or ‘black’ (rather dark brown) after firing. Due to the industrialized process, the tones are generally the same every time.