Universal indicator is a pH indicator that transitions through numbers 3-12 (on the pH chart) to indicate the acidity or alkalinity of solutions. Although there are a number of commercially available universal pH indicators, most are a variation of a formula patented by Yamada in 1923. Details of this patent can be found in Chemical Abstracts.
Experiments with Yamada's Universal Indicator are also described in the Journal of Chemical Education.
Here are the colours that indicate the acidity of a solution, after adding UI:
1. Very acidic - Red
2. Acidic - Orange/Yellow
3. Neutral - Green
4. Basic/base/alkali - Blue
5. Very basic/base/alkali - Purple