After double-checking each and every wire, I finally found the problem.
The very first LED was apparently defective.
As a test, I simply connected a spare piece (~ 10 LEDs) – and lo and behold – colors and effects were now playing correctly. Then I cut off the first/starting LED and soldered the setup to the second LED. Tested again - COLOR - effects are playing correctly. To complete the setup again, I simply extended the end by one LED. It's working perfectly so far.
Thanks for all the help and great suggestions! May your LEDs always shine bright! 🙌




