In an experimental approach pupils should explore in a hands on chemistry project different plant colours in acidic, neutral and basic solutions with the aim to find the best acid-base indicators. The experiments are going to be documented by fotographs and text and published in a PowerPoint presentation or web page. The pupils of the different schools should experiment with different plant species starting with room flowers and then expand the research on local wild flowers. In a possible second step the chemical and biological meaning of the ability to change colour could be surveyed by the pupils.