First have your child sort the hearts by color. Then have them place them on a graph. After you check their work you can have your child actually stick the sticker side of the heart on the graph. To further extend this lesson ask questions like which color heart do we have the most of. How many pinks do we have. How many more pinks are there than purple. How many less pinks are there than reds etc.
I must admit Little Sweets is too young for these older preschool/kindergarten activities, but you have to remember that I taught these two grade levels and absolutely loved it. I am still trying to retrain my brain so that I can think of more developmentally appropriate activities for Little Sweets. While I still have these ideas popping in my head I thought I would share them with you so that you might be able to do the activity with your child.