Listen to your architect. Grey/silver looks clean and will never date. We took our architects advice and went with silver. I like the fact that they blend into the scenery and house and are not a feature you see. I do not even think we had aluminium frames mid 20th century. Wood?? Black frames I believe became popular decades later.

We are wanting to do the same thing and have been having trouble finding examples of others using a light roof with black windows as it seems the done thing is dark roof dark windows etc. But I've found the following here on Houzz which I think shows it can work. I love the interior look of black window frames because they "disappear" and allow the view to take centre stage. Alternatively some window manufacturers can produce a different colour on the exterior and interior for you (although I think they are only on double glazed units).

Hello jo Louise Can you please post a pic sometime today? We need to make an urgent decision re this to sign off the windows so I would love to see how it turned out. Thanks

Either will look great on external part of our house, as we need to choose between the two based on the interior which is quite neutral (wood, light neutrals, accents of colour that will change over time). We want the window frames to be versatile so as to not clash with changing colour schemes but a bit worried that black will be too hard and stark.