From what I gather, with the right color setting method, the IKEA Trådfri gateway can set the color temperature of the temp adjustable bulbs with no steps, but the current implementation in HA only gives access to the three preset color temperatures.
If it is possible to implement this it would be possible to change the colour temperature gradually during the day which would be pretty cool.
Do you have a source for this? We built pytradfri based on what we could reverse engineer from the app and there was no sign of what you mention there.
Also, if it works, we would need to implement it upstream in the pytradfri-lib before it can get into hass.
I just tried out your library, it does seem like it switches fairly seamlessly if you run the following command in the pytradfri api, changing the values for X and Y:
api(lights[5].light_control.set_xy_color(39000,39000))
Tried it with several different values which seem to independently dim the different coloured LED’s.
The negative side is I do get some timeouts if I hammer the command too often, so it might not be practical as it stands to do quick color transitions through many values.
Ah, that’s good then! 
I’ve read user reports about the gateway crashing if you send to many commands to it. Fingers crossed it’s something that IKEA fixes for future releases of their software!
I don’t think that is possible: Look at the bulb when changing the white point, you can observe that it turns on a different set of diodes, especially on the bulb with opaque dome.
It does, but both sets of diodes are independently dimmable, so the combination makes anywhere in the color space where the two diode colors intersect available - the problem (I think) at the moment is that HA doesn’t use the color space command to select the color, and from what I can gather the RGB command only exposes the three preset color values.
If I get a little time in the next few weeks I’ll try and see if I can make any sense of the HA component to see whether I can make it call the color space command instead which should allow individual adjustment.
Great! I’m also interested to have fine color temperature control of Ikea lights.
I just tested Hue & Me LITE app for Android and it can also set custom color temperature for Ikea lights.
Work has kept me busy sadly, so haven’t had time to look at it, but I just saw someone requested a merge in the underlying library that will make fine control possible in kelvin, which would be really neat, he did say he wanted to integrate it into HA too, so hopefully he will get it working
That’s a good news! I can hardly wait to see it working! 