Wood for the wheels supporting the test tubes
String or wire to hold them up
Food coloring (water-based works best, but any kind will do)
I ordered my test tubes via Carolina Biological Company
They sell boxes of 48 test tubes for around $10 to $15 and have decently priced shipping. A good company!
They also sell universal indicator solution (not great quality, but still decent) if you want to use the chemistry approach.
A 1/2" drill was used to drill the holes for the tubes
a bandsaw was used to cut the circles for the wood form (use whatever you want here though)
and a tiny drill bit was used to drill holes for the string