Is there a coloured ( dark Brown ) wood preservative that protects new wood from rot, decay AND insect attack as well as being water repellent ?

yes Barrettine do a dark brown microporous wood preserver that protects all wood from rot,fungi,mould and insect attack and because its microporous it shouldnt flake or blister. Brewers will do a wide range of preservers or pop into Dulux or Crown decorating centres and they can help

Hi there if you use a oil based woodstain and give the wood 2 good coats this will protect the wood from all you've listed Sikkens or Dulux weather shield will be perfect for the job. James Can-Dec

there are a number of coloured preservative stains, Cuprinol, Sikkens, etc. some diy stores have their own make, B&Q, Wickes, Wilkinsons. before applying it helps to pre treat the timber for better coverage. For oil based products coat the wood with a light covering of turps or white spirit, if water based spray the timber lightly with a hose. This stops the brush dragging and helps an even coverage.