Greyed out dual colour mesh switch

Hi .,
I’ve a strong feeling I’m doing something wrong but whatever model I download to Luban , the colour meshing option is greyed out.
I’ve searched for the error on my part but so far nothing seems to work .
Anyone care to help me
Thanks

Dual you have the dual colour print head installed, and selected in Luban?

Hi
Yes all set up , I had changed my two nozzles for ruby tipped ones .
So I wanted to test them out .
I picked a model at random small enough just to test and no way could I get that option to print dual filaments or colours.
It stayed grey .

I managed to get it working today but it seems like it’s intermittent or maybe it’s me that’s intermittent!!.