The heroku-side code for experiment 2 described in the article:
Bazilinskyy, P., Dodou, D., & De Winter, J. C. F. (2020). External Human-Machine Interfaces: Which of 729 colors is best for signaling ‘Please (do not) Cross’? In Proceedings of IEEE International Conference on Systems, Man, and Cybernetics (SMC). Toronto, Canada. https://doi.org/10.1109/SMC42975.2020.9282998