I like existing brick but not that shade of green so I'd clad new extension in complementary colour to brick walls that aren't to be extended and I like white windows if roof doesn't need tiles replaced repointing etc I'd leave You could do basalt colour gutters etc and cladding with white trim on gables and depending on views light have some more modern perhaps double glazed windows on extension. Windows need to be all same colour on the front wall eg white painted timber if that's what your existing colonial windows are but don't need to be same shape. Just some ideas

I actually really like the fence... it gives it a country australiana sort of look. I prefer it open to a fortress of corrugated iron. Look, there's not a lot can be done to change the house... it would look even more of a hash. It IS the style and age it IS and it has a charm of its own. As long as it's all tidy and in good repair that's great. It's a good solid house by the looks of it. Instead focus on landscaping the yard. Pull the eye forward to the fence line with some plantings on either side of the wire fence. I'd do a low floral border that sits belownthe top of the fence and then maybe something like agapanthas on the other side so you can appreciate them from the street. I'd favor natives like grevilleas and bottlebrush. large shrubs flowers in a large bed in front of the house. I'd maybe put a few standardised bottlebrushes on either side of the path for height. It would all bring the gaze forward to the lovely native garden which would attract birds. natives tend to have shades of grey in the foliage which would look good against the roofline which is more dominant anyway. https://www.abc.net.au/gardening/factsheets/cottage-garden-natives/12904492 https://www.australianplantsonline.com.au/blog/post/cottage-garden-with-natives

Try any of these. You have dark window frames and they look good against the brick. I would prefer for a solar passive solution for you to have Colorbond shale grey or similar for your roof tiles. And the trim everywhere else in Dulux Ticking. But it depends where you live in Australia to whether you have extensive days of hot sun.

The roof is a very big part of the exterior of your house. Faded concrete tiles, even cleaned ones ,will always make your house appear old and dated, no matter what else you do. I would definitely paint your roof, probably in a charcoal colour like monument, as it not only looks modern but is neutral and will complement whatever colours you use elsewhere. If you add solar panels, they will also blend in well. Using a green shade on the roof is the last thing I would do. You would instantly date the house as it was typical of probably the eighties and you will severely limit the other colours you can use.