Set startsettings or change current settings for Items (Color, brightness) with command

[sihui]

Your items definition looks correct, although you cannot use Number with Lighting:
http://docs.openhab.org/addons/io/homekit/readme.html

Did you forget to search for new devices via Alexa or Alexa App or Alexa browser login?

Edit: or maybe you can use Number with Lighting, don’t know, haven’t used it yet:

@digitaldan

Lighting, switchable and thermostat tags are currently supported (although not limited to those types of items).