Possible Clues:

• Kind of paper or test
• Acid or base indicator
• Test paper
• Shed light on rising problem for test paper
• That'll show you 2 down till all is blue
• A CID matter? There you have it in red and blue
• Acid-base indicator
• Acidity tester
• Substance used to tell acid from alkali
• You may take it as red if it's a CID matter