Unfortunately it will not work that way 
During implementation the DIRIGERA gateway shows it’s badass behavior. Setting color while bulb is off the command is acknowledged AND confirmed by the gateway. But in fact it doesn’t work.
You can trick also IKEA App with one curl command setting color e.g. to red while it’s off, then switch it on via app. Bulb is shining Hulk Green while App thinks it’s Ferrari Red. Reproduction rate is 100%.
So currently color cannot be set in beforehand. Next difficulty is to adjust color and brightness when switching on. Doing this very quick results into inconsistencies - color or brightness will not reach their target states randomly.
Finally I ended up to present a switch on sequence based on fadeTime which is now present as config parameter with default time 750ms. In addition you can define the sequence if first brightness shall be applied and then color or vice versa. If light is switched on you’ll see the adaptions during fading but I see no other solution right now.
IKEA has a lot of things to do on their gateway!