I cant help with the color, but just a ’pro’ for mahogany vs pvc, the pvc can get very hot in the sun. The real wood doesnt have that issue.

I hope you get a good answer here. Your garden sounds lovely.

(also, dont stress if somone insists on pictures. your dilemma is pefectly clear from your description.)

I don't know about staining, but how about an outdoor rug on it?

Get your contractor to apply stain to several pieces of the mahogany he is using to construct your deck to see how well the wood will accept stain and what the results will be like. Wouldn't recommend painting your deck as the paint will wear rather quickly with use. Another way to "hide" a portion of the mahogany deck is to use an outdoor area rug. Hope you find something that will work well for you and good luck!

@auntthelma it faces north so no direct sun hits it

The mahogany will fade very quickly- in a month it will have faded and by next year it will be turning grey. Yes you can stain mahogany, just test it on samples first.

@Norwood Architects i was thinking a semi-solid stain like BM Arborcoat

@HALLETT & Co. even if deck is on north side of house it will fade that fast?

IMO we need to see pictures. Often something new just needs time to have you get used to it. IMO real wood would have been my choice not faeplastic wood that IMO does not suit the garden and home you describe. Post the pic here in a comment maybe 2 pics one close up of the wood . DO NOT start another post.

I do not agree that this is clear we have no point of reference as to how this even looks .