These dots will fade in colour when you start to over play a song, they will be listed next to your songs.
notification on new feature.
How your playlist will look at first. You will always see your friends' song colours and you can click on the dots to recommend new songs.
When you click on the bubble gum machine it will show your colours, when you shuffle a playlist it will prioritise the songs that you don't play as much. There is also the lightening bolt button which you can click to change the song as many times, and the rewind to reset it back to the original one.
If you click on a song you are overplaying you will be notified and Spotify will recommend a new song to listen to.