Here is my own rainbow of sari petticoats. To wear a sari, you need to wear one of these to tuck the sari into as you wrap it around your waist.
This and the choli are considered underclothes, so running around with just these on is considered a faux pas in India.
These petticoats come in so many different hues. Depending on if the sari material is transparent or not, it really doesn’t matter if the petticoat is the exact same color.
I actually had the good luck and maybe the eye to pick out the perfect shade of pink for my georgette and chiffon sari without even bringing it with me to the store.
Another reason that a petticoat should match your sari is that the lining of the blouse might have a different texture.
For example, this nice vendor at the famous Laad Bazaar near Charminar in Hyderabad, gave me some sparkly lining to make a blouse and petticoat with. Upon doing petticoat shopping, I almost bought a new dark purple petticoat, but then remembered that I wanted both the blouse and the skirt of the sari looking sparkly.
I haven’t received a lot of extra lining from vendors so I don’t know how common this is. But I do know that the petticoat is often sold separately and can be found at almost any sari department store.