When we put lemon juice on the common salt it turns to bluish violet colour.Why this thing happens? Share with your friends Share 1 Mehul Pahuja answered this Because salt contains starch when lemon juice is added into it. It changes to blue-black, because of iodine present in lemon juice. 2 View Full Answer Abhinav answered this it releases the iodine -1 Ayushman answered this Because salt contains starch and when lemon juice is poured into it the starch colour changes to blue-violet 2