What a gorgeous color! Volunteers are such fun. I had a lettuce emerge in my gravel path one year, and I just let it grow. Seeing a head of lettuce sitting on the path provided no end of amusement.

Is that color similar to what you originally grew, or is it something new?

Lelia, yes, both colors are same as parents. The Dahlberg Daisy is a native, only comes in yellow, and the original petunia was the same color. You're lucky, having lettuce volunteer. I can imagine what that looked like. I've had that happen once in about 20 years of growing it!

Glad I read your post first. I was just going to post the same thing. But in my case I had 3-4 petunias in an area last year. I took a small paint brush and pollenated them by simply swirling the bush inside the flower. The brush became full of pollen so I transferred some, for sure. I was lucky I got about 5 seed heads which I harvested. I say lucky because some of these were supposed to be sterile.
Anyway I misplaced the seeds. BUT this spring my bed was full of petunia volunteers. I have every color possible and some very beautiful blends. Even a polka dot petunia. I am busy swirling the brush again this year. But I will not harvest the seeds. It is better if they drop to the ground on their own.
I did find the seed pods ultimately and planted the resulting seedlings around the yard. Great colors.
Bob