Custom Orb looks great. But.....your flashings and trims can cost a lot of money and labour to finish well. If you use it in a few select areas that need little or no flashings then it works better. It becomes even more of a 'cool' feature then as well. Installing it vertical rather than horizontal could be much easier to install as well. We cladded our house in it about 7 years ago. While it looks great I probably wouldn't do it again due to the cost (and mucking around..) and also the fact that a change of colour isn't a paint brush away...... My preference would be FC sheet with battens over the joins, a bit of Custom Orb in a few selected areas that are hard to maintain/paint/etc and good old face brick. Recycled bricks rather than new would be a nice feature as well. Face brick needs little maintenance and doesn't damage easily from kids running into with bikes, etc..

My only comment might be that monument is grey and a nice strong grey but Lexicon is blue based, so I'd look for a gray based white or builders white which apparently has very small touch of black in it albeit it is still white. I think this would keep the undertone matched. For instance, I love green and although I probably won't paint the interior of my home green, Whisper White has a slight green undertone, so even though it's still white, it has the colour tone that I like.

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

Thank you for your comments everyone, much appreciated. I am leaning towards Monument for the windows. The house is a late 70's build and the extension is at the back of the house. The extension is really just filling in the outdoor area to make it an all season room. We will be cladding the west side and then have double glazed windows/sliding doors on the north and east side. I like the look of the Axon cladding. We will use the same cladding for the front of the house because we are also changing our front entrance to enable us to turn our study into a 4th bedroom.