Planning hour-long art lessons for Kindergarten students can be tricky, because it's difficult to imagine what activities they will do quickly and what kinds of activities will take them a longer time to complete. So, I try to have an additional, simple activity to extend the time for those students who finish faster than I would have expected. I could have them just read books or draw pictures, but I like it better if they can do a second activity that matches the lesson.
Thus, the birth of the purple pictures. First, I read the book "Harold and the Purple Crayon" by Crockett Johnson, having students notice what Harold does with his purple crayon. I explained that they'd do a line collage first, and then if they had time, they could draw some of their own purple pictures. Some students really got into it, while others simply filled the paper with scribbles and lines. Later, I had some of the students tell about what they had drawn. I pointed out details in their drawings that added interest, such as stars in the sky, or facial expressions. This turned out to be a perfect addition to the line collages they did the same day.