It all depends on the indicator that your using to measure the pH! Look at the wiki page of Ph indicators which gives you an idea of the chemicals that they use as indicators and the colour they change!
As Julia says it depends on the indicator you are using what the colour changes are – things like phenol red, pH paper strips etc are different things you might have used in school.
It depends on the way something of a particular hydrogen ion concentration reacts with the particular indicator dye! 🙂
Hi ryanmccabe! PH indicators do change different colors depending on the type. But the reason they change is because of the chemical reactions they undergo. Different chemicals will react differently depending on the basicity or acidity of the solution which means that a pH indicator is a chemical detector for hydronium ions (H3O+) or hydrogen ions (H+) that contribute to different basic or acid levels. There is a decent description of how it all works on wikipedia: http://en.wikipedia.org/wiki/Acid-base_indicators. Sounds really cool!