Light fascia, a not quite white, but very light colour that matches the yellow house - maybe the colour on the knobs on the platform. Same light colour for the posts & rails of the deck for all except the very top hand rail leave that grey. Like the first picture in the comments. Paint the end board on the bottom stair platform the same colour as the house. Grey stairs perhaps. Leave knobs light.

We're building too this year and our exterior colours are light & dark grey... couldn't afford the timber cladding :( ... and we are having black alum windows, so I say go for black! :) Black windows suit most facades, from the contemporary to the more traditional... Plus what's your alternative, the alum silver? That would look even more blend against the grey exterior colours... whereas black will make the windows a stand out feature of the house... If you're concerned the facade may look a bit drab and if you're game enough, then be bold with a pop of colour in the front entry door... Internally, the black windows (against white/light walls?) will frame the outdoors looking almost like a picture... And no, you are not stuck with a monochrome look inside... you can easily introduce timber (floors, furniture, etc) to create warmth, or any colour you want as black goes with everything... Good luck :)

No, not on the same wall. It is possible to have different colours inside, in different rooms, but outside, each exterior plane should be consistent.

Agree with above posters, remove the lacework from the portico and even the railing (although cant see it too well) I would also remove the large bush in front of the door and in the centre of the front wall and replace with a one or two tall and large statement plants in pots (dark/black/charcoal coloured) and plant out the garden bed with the same plant the full length, maybe a lavender or something to add a pop of colour. Also add good mulch to both garden beds and a bit of a general garden tidy up will help. Adding a top coat to the lawn will pay dividends at this time of the year! If there is any loose or uneven pavers, fix those up. Potential buyers are always looking for clues to gleam whether the house has been well looked after, and these small details can sometimes be a deterant. I think your house looks grand, not boring. If there is a porch light, maybe update that to something black and modern to reference the dark in the pots and a colourful new doormat. I cant see your front door, but if there is no security screen, paint the door a striking new colour which references your internal decor. As others have said, try to spend as little as possible as, there is no guarantee that the extra spending will be reflected in the sale price. All the best with the sale.