A list (from Wikipedia) of some common pH indicator solutions.  We used Bromothymol Blue in the acid rain demonstration.
Indicator Low pH color Transition pH range High pH color
Gentian violet (Methyl violet 10B) yellow 0.0–2.0 blue-violet
Leucomalachite green (first transition) yellow 0.0–2.0 green
Leucomalachite green (second transition) green 11.6–14 colorless
Thymol blue (first transition) red 1.2–2.8 yellow
Thymol blue (second transition) yellow 8.0–9.6 blue
Methyl yellow red 2.9–4.0 yellow
Bromophenol blue yellow 3.0–4.6 purple
Congo red blue-violet 3.0–5.0 red
Methyl orange red 3.1–4.4 orange
Bromocresol green yellow 3.8–5.4 blue
Methyl red red 4.4–6.2 yellow
Methyl red red 4.5–5.2 green
Azolitmin red 4.5–8.3 blue
Bromocresol purple yellow 5.2–6.8 purple
Bromothymol blue yellow 6.0–7.6 blue
Phenol red yellow 6.4–8.0 red
Neutral red red 6.8–8.0 yellow
Naphtholphthalein colorless to reddish 7.3–8.7 greenish to blue
Cresol Red yellow 7.2–8.8 reddish-purple
Phenolphthalein colorless 8.3–10.0 fuchsia
Thymolphthalein colorless 9.3–10.5 blue
Alizarine Yellow R yellow 10.2–12.0 red

These indicators are normally used over a fairly short range of pH values (indicated in the table above).  As a pH indicator, bromothymol blue, for example, would be useful between from about pH 6.0 to pH 7.6.  Other indicators work in different pH ranges.



Using bromothymol blue you wouldn't be able to distinquish between an acid with pH 4 from an acid with pH 5.  They would both appear yellow.  Similarly solutions with pH 9 and pH 10 would both appear blue (vivid blue).  With bromothymol blue you could hope to identify solutions with pH 6.5 (yellowish green), pH 7 (green) and, and pH 7.5 (bluish green).