The black dot (Kandinsky section) was the first I liked, a lot. Red, if you mean the red cross, the violin? Or the red dot
What didn't get my attention was the sad (I think it was purple) - edit, light violet, saw now.
EDIT: I went back now to the tool and checked on the red you asked for, so the red in the section Hear the painting is super, with all those very low bass sound playing, but as well, the same when you are in the try it yourself, that is the red - nice violin I thought. So both are great. The blue I liked and connected the most was the big blue in try it yourself and in hear the painting too.
As I said, more time would be needed to explore all the combinations from there :)