The water solution of iodine turn blue litmus paper to red.
pink
Litmus paper turn to red color.
It would turn Green
dark green
If it is pure water, it doesn't change.
In a neutral solution litmus has a purple color.
The color of litmus paper in acidic solutions is red.
Red color in acidic solutions and blue color in basic solutions.
as rain water is slightly acidic so will turn the blue litmus paper a little red.
Coffee has an acidic pH - red with litmus paper.
I believe, that acid makes blue litmus paper turn red.