I think this may already be on the list but it would be very useful to have a Send Status Request button for RGBW lights - it is present on non-RGBW lights.
Also, if the Color Controls pane was enhanced (made deeper), it would be very useful to have a slider like the W (White) one for Infra-Red so that lamps with Infra-red lamps could be adjusted from the UI.
It leads to a general question as to why the Device control panes are so small - they get lost on my monitor! Just joking but these days there is an awful lot of screen real-estate that could be leveraged.