Which undercoat to use

Hi all;
Got a timber back door to paint (as soon as it stops raining)........Grrrrrrrr

Currently painted with a brown gloss, it needs a good sand down and a bit of filler here and there

Going to top coat with Dulux Weathersheild exterior gloss - Conker

After priming bare timber and filler, was planning on undercoating the whole door with Weathersheild Undercoat, but is there any preference to use white or grey undercoat as finishing with a dark colour

Know that you use grey under black but not sure when using other dark colours, ie Conker

Thanks for any advice guys

 

Thanks for reply JJ

Will go with the grey undercoat and was gonna follow with 2 topcoats - just think 2 gives the timber more protection against the elements

Cheers again