An Easter activity that you could connect with pH and indicators

Dyeing Easter Eggs the Natural Way | Food & Think

Food dyes can be used to explore the effect of pH on the color of the dyes. Because most food dyes can also behave as indicators, it would be easy to set up an experiment to determine why egg dyeing instructions always recommend that you add vinegar to the water. You could make the egg dye at three different pHs. 1. Water plus vinegar  2.  just water  3.  water with something basic that can be easily handled, such as sodium bicarbonate 

Questions to ask:
Are the dyes different depending on the pH?
Are some food dyes more sensitive to pH?
Which dyes have the most intense color?
Could the vinegar serve more than one purpose when dyeing eggs? Hint: Egg shells are made of calcium carbonate. How does an acid react with calcium carbonate?

The best chat I have seen that shows the colors of foods at different pHs (thereby, acting as indicators) is Chemical Demonstrations, vol. 3 (the green one) by Shakhishiri. It's a great volume but a bit pricy for most teachers.

Web resources
Here's a free website that has descriptions of some of the food indicators. http://antoine.frostburg.edu/chem/senese/101/acidbase/faq/household-indicators.shtml

Video clip that shows food indicators in use
http://www.bbc.co.uk/learningzone/clips/food-as-an-indicator-of-ph/122.html

Shakhishiri's website of chemistry resources
http://scifun.chem.wisc.edu/