There is no channel because there is no need for a Channel. You can just send a PercentType value to a Color Item and it will adjust the brightness. Similarly, you can turn on/off the light by sending ON/OFF commands to it as if it were a Switch Item.
So put the ColorItem on the sitemap using a slider and it should just work, no Rules required. Just make sure to configure the slider to only go from 0-100. I think that’s the default but just in case doulbe check in the docs.