Turmeric is a type of powder which belongs to the ginger family and is called Zingiberaceae. Turmeric is used both as a spice and as a natural Dyce also. The yellow color of turmeric is due to the presence of compound curcumin.
This compound which is present in turmeric is due to hydroxyl groups. This compound does not undergo any change in an acidic medium but it changes in the basic medium.
In addition to this compound, there is another compound called phenolphthalein which resembles this substance. This phenolphthalein is colorless in nature. Both this substance does not change its color in acidic medium but in a basic medium, turmeric turns reddish brown and phenolphthalein turns pink.
Another substance which does not changes its color in basic medium but changes its color in the acidic medium in methyl orange. It turns pink in acidic medium. Thus, turmeric powder turns red because slaked lime which is nothing but calcium hydroxide is added to it and it becomes red. When any such substance will be added to red turmeric will turn yellow. This is the reason why turmeric powder turns red when mixed with slaked lime.