I had the same problem too.
Do repeat the descaling with water only. After the descaling the Lattissima shuts down. Just wait some time after shutdown before restarting the Lattissima again. The orange light will be turned off.
Hope this helps you too!

Our machine's water hardness may need to be reset or your machine may need to be descaled.
By default, the machine is set to the hardest water setting, so it may prematurely alert you to descale, as indicated by the orange cappuccino light. When resetting the machine to factory settings, it automatically changes the setting to 'hard' water.
If you recently descaled the machine and are finding that the orange descaling light is still illuminated, please change the water hardness.

You may modify the water hardness setting by following these steps:
For the Lattissima Plus machine:
Begin with the machine turned off
To set the water hardness to soft water
Hold down the Latte Macchiato button while turning the machine on
Once this is done, the orange descaling indicator light will come off.