Alexa shades of white don´t work


I have RGB WLAN bulbes connected to Openhab and setting color over the UI works fine.

I have also added the Alexa skill and i am able to set colors like green, red, blue,… with Alexa. But when i try to set it to white or warm white, it says that this isn´t possible with my device. Why do only a fiew colors not work? However these colors had already workt, when i tried it half a year bevore.

Can anyone hlep me?