[Kleftiwallah]

Good afternoon everyone,   I have just unloaded my Astravan load of 75% rotted horde muck in buckets onto my FINAL raised bed.

There are litally squillions of blood worms still at work in there, so the composting process is still ongoing. Now to the question, (you had forgotten about that hadn't you?). 

Do I cover the 'good stuff' with black or clear plastic to ensure the best conditions for 'my' worms so they carry on the goodwork over winter?

Over to you,  Cheers,  Tony.

[New shoot]

They will prefer black plastic so they feel safe, but weed membrane would be even better as it lets rain through.  If the manure dries out, the worms will not be able to do much with it.

Not an answer to your question, but something kind of linked to it.  One of my plot neighbours covered a lot of just bare soil with clear plastic one year and they got huge sheets of liverwort and algae growing on the soil surface.  It was quite a sight to see.  It just shows how many spores there are lying around waiting for the chance to grow   

[Subversive_plot]

I wouldn't put plastic over manure or compost that you want worms to stay alive in. It could go anoxic, kill the worms and start stinking.

A breathable geotextile fabric might be OK, or just top with grass clippings or other mulch.

[Kleftiwallah]

Many thanks for those interesting answers. 
I shell keep a close eye on the little darlings.

Cheers, Tony.