What style is your garden?
Are you at all concerned about resale in the next decade or so or is this just for you?
How are the rooms that have views to the conservatory styled/decorated?
What colours do you actually like yourself?
I’m assuming that pretty much any RAL colour is your oyster in this context.
I think white or even cream would be as dated as the wood effect is so would be a no from me.
Black would be too harsh I think if it’s not a modern build/extension or going for an industrial look.
Grey a more up to date choice, as long as you’re not personally feeling grey-overload at this point, I don’t think grey will instantly date as it’s a very long term trend, but find a warmer toned mid-grey to avoid the harshness issue, nothing too dark. Not anthracite!
Other warm neutrals taupe/greige/fawn type shades, like Collette suggested from the brickwork but maybe looking for pinker tone rather than yellower tone, could be a consideration if you want to try to blend out the difference between the conservatory and the original building. It would be nice and modern and uncontroversial, a more seamless transition from the stone to the frame. A decent option I think.
Or, colours!!! I love making bold statements with colour so depending on context personally I might consider violet or fuschia or teal or jade, pairing it with lush tropical planting outside and in, colourful flowers and fruits, eclectic painted furniture and patterned textiles and mosaics etc....or, for a more subtle approach, a more muted tone - now, I think sage green is a really lovely colour, but, kinda overdone in cottages and gardens. It’s the expected colour for this kind of thing. So how about something different, like powder blue? Same effect as sage green, subtle colour that doesn’t detract from it’s surroundings, but it’s something different from the standard cottage garden sage green.
Would love to hear how this goes! I have some wood effect uPVC doors to our garage/outbuilding that I want to paint, will be doing it myself though. If you’re getting a professional in to spray I would be very interesting to hear the practicalities of it all.