I asked question below which you kindly answered. Follow-ups: the doors are currently a weathered green cuprinol finish - does affect your suggestion? Also I am in the countryside and in the North - would solvent-based be a better bet than water-based? Which paint would you recommend in Chartwell Green for exterior wooden driveway doors? They are next to a garage toller door in upvc Chartwell Green - is the colour in exterior paint likely to be close enough to match? Assuming the timber gates are bare, clean, dry, sound and prepared as detailed in the technical data sheet you could consider Zinsser Cover Stain followed by 2 coats of Zinsser AllCoat Exterior (Water Based). This can be mixed to Chartwell Green aswell as many RAL, NCS or BS colours in a matt, satin or gloss finish.
On a previously painted substrate we would recommend to test on a small area once prepared for compatibility and adhesion prior to full application.
Water based is more tolerant to previously applied coatings, assuming the temperature for application is above 10°C it would be best to use water based.
If the temperatures are below this we would suggest solvent based.