Red cabbage juice can change colour.  The red colour of the vegetable comes from a red pigment in the plant (called anthocyanin).  It is the same substance which gives grapes, plums and apples their colour.  

What's going on?
The juice acts as a pH indicator for acids and alkalis (it can change colour depending on how many hydrogen ions are in a substance).  You can do this at home easily (but watch out for staining). Many other natural dyes and indicators are present in strongly coloured plants and vegetables.

We made juice and tested different household substances to see what colour it turned.  

Children analysed designs of several different towers and supportive structures looking for clues in their design.  They were tasked with making the strongest tower (not the tallest) which could support a small mass (the weight of a reading book) unsupported.
Perhaps the best part (for some) was being able to eat some of the structures at the end!
Here is the gallery of our work: