I reckon you should go for a bright colour rather than the greys. Greys can look a bit boring after a while. Mainly due to their popularity as every second house I see is grey and just about every house I design the owner wants grey..... A client recently used 'Vanessa May' with Monument roof, facias, etc. and windows. The architraves in white. 'Vanessa May' is a mid violet and I got to say it look's bloody great! It's a similar size cottage as yours as well. My last client is using Dulux 'Pink Poppy' on their renovation and addition! However the job I started today has already been specified with a combination of greys...... That green you have is a great start.

hardiplanks linea boards They sure look the same!

nothing wrong with a mixed but balanced materials palette.....we regularly mix weatherboard cladding with rendered sections, but it comes down to how it's configured and the form articulated....the problem is when say only the lower level is render and then you have a lightweight upper form articulation - it screams obvious upper level add on, rather than seamless extension.......... It's always about balance and texture - on your home the tiles provide a nice complimentary textural contrast to the render.....you pull this out and replace with a more streamlined contemporary material you'll get a different look - it could well work, but as always when we deal with these types of project we try to respect, preserve and derive the solution form the original character as much as possible........ If you are using an architect specialising in this type of work then it sounds like you are in good experienced hands and rather than confuse the process for yourself you'd be best to work through the options with them privately - it can be almost too confusing and overwhelming the you get multiple opinions, particularly say from here where your context and the project subtlety/details are not fully understood... Best of luck with it Cheers PD :)

Colorbond steel needs no additional finishes is quick and easy to install, looks excellent, easy to replace any damaged sections and needs no ongoing maintenance or future painting...what's not to love?