Hue changes but not colour.

  Hello @Bills. 

If smart bulb will not change to other color, please try factory reset bulb and see if that helps:

How to reset TP-Link Kasa smart bulb?

Can I know which color the bulb will not display? 

  @Solla-topee 

I have reset the bulb and tried it in different rooms    .

It won't display any colours, just turns off when the colour wheel is used via the app. 
 

The warmth of the normal light will not change either. 
 

thanks!

  @Bills.  thanks for more case details, it sounds to be a defective unit, you could check warranty with the retailer.