Lemon cupcake with curd filling

I.made.cupcakes for my friend Jasmine her grandmother passed away suddenly at 82 years old.
She liked purple and I hoped to make a purple icing looking like purple hydrangeas but once I added lemon juice to my purple icing it began to get a blueish Color. She was still happy and they look pretty.
I made a white cake mix
With the 1/2 cup oil
1 cup water ( used lemon.juice instead)
3 eggs ( I added one.more ) so 4 eggs total
Zest of two small lemons
Preheat oven to 350 then reduce to 325 before baking the cupcakes in a.liner on top rack for 20 minutes minis were about.15 to 17 min.
For icing I whipped two cubes of.softened salted butter
Stop mixer and pour in a 2 pound bag of powdered sugar
Slowly add 6 to 8 tbl of fresh squeezed lemon juice and zest of two small lemonsi needed almost 1/2 cup of juice for it to get the right texture I needed to pipe. Whip and few minutes stopping to scrape down the sides. I added a good scoop.of violet gel wilton. It was turning blue lol