This might be a larger issue, but the Clue is the only BLE-capable board that I have at the moment.

The ToneService part of the Bluefruit Playground example doesn't seem to work when connecting with the Bluefruit Playground iOS app. It also doesn't seem to work with the Web Bluetooth Dashboard. The corresponding service in the Arduino version of the Bluefruit Playground firmware does seem to work.

Adding debugging print statements to show the value of tone_svc.tone seems to show that it's always None.

A stripped-down script that only advertises ToneService also does not work.

Does this work on other boards? Any debugging hints?

The main difference I can see by reading the code is that ToneService uses a fixed-length characteristic, while AddressiblePixelService is not fixed-length.