@Linda_Owl – Food dye is typically what most manufacturers of pink lemonade use today. You can also add a bit of red food coloring at home to basic yellow lemonade. However, in the past that was not always the way to make pink lemonade. The Oxford English Dictionary says:
“pink lemonade n. chiefly U.S. lemonade coloured with a small amount of grenadine syrup, or (sometimes in later use) another natural or artificial colouring.”
There are several different origin stories about pink lemonade. All say it originated at a circus in the mid 1800’s but the name of the inventor varies and so does the means of invention. It perhaps was the result of someone accidentally dropping red candies into the batch and not having time to make another, thus selling it at a premium as special “pink lemonade.” It may also have been the result of something red accidentally coloring water pink. By various means this ended up being the water used to make that days lemonade, which sold out quickly for being different.
However, most recipes for home use suggest juice rather than food dye. Most recipes I see now say to use cranberry juice, but I have had strawberry lemonade, cherry lemonade, and raspberry lemonade, all of which are a lovely pink color and having a slightly different taste from yellow lemonade. My mother generally used grenadine syrup (a sugar syrup originally flavored with pomegranate juice) as in those days everyone had some around in order to make cocktails at home.
Wikipedia sums it up as follows:
“Pink lemonade is simply lemonade that has been dyed with pink coloring and is sometimes made sweeter. Sometimes artificial colorings are used; natural colorings can include grenadine, cherry juice, red grapefruit juice, grape juice, cranberry juice, strawberry juice, pink-fleshed Eureka lemon juice, or other juices.”