An indicator that turns RED in acidic solution and BLUE in basic solution is:

1. Litmus is the classic red↔blue indicator. 2. Red litmus turns blue in BASE; blue litmus turns red in ACID. 3. Phenolphthalein is colourless in acid, PINK in base. 4. Methyl orange is red in acid and yellow in base. _Source: syllabus Science Ch 2 §2.1.1 Indicators_