Hi, I know there are so many things to take into account and it's hard to get perspective from a photo. The white you can see is an extension with building paper, and the red is the existing building which is two story. The exterior is wide weatherboard planking, the windows are silver aluminium with very little trim. The doors in the front of the picture are French doors from bedrooms that will open to an enclosed courtyard ( yet to be built of course) The roof will be a light grey/brown but you won't see it much because of the flat roof style. There will be decking and ballustrades covering half of the new extension.

There's a few but Google Sketchup is probably the most available. The thing is, you'd be better off dealing with your architect for this because they would be better to tell you what materials are actually practical, they would know costs, installation times, etc. For example you might not be able to do a lot of masonry in heavy seismic zones and certain other types of cladding may require thicker foundation, etc. Not only that there are a myriad of different ways to stucco a home and so forth. I mean you could use Sketchup to mockup some ideas, but this is work that is honestly best done in concert with an experienced professional.

To answer your question I would paint the body of the house blue, all trim white, and then the "fringe" which I think ties into your porch decking, I would paint it the gray. It is a good "grounding" color for your home. Sherwin Williams has a cool web tool. Take a pic of your house and load it onto their site. You can "color" away on your house. When I painted my house for the first time, I did not want the garage door to stick out, wanted it to blend into the house. Everyone said it would look weird, needed to be painted the same as the trim. Used the Sherwin Williams site and realized want I visioned looked good. I have neighbors of dubious design skills! Ha! Ha!

With any post war house built in the 50's the connection from in to out is non existent. Depending on where living rooms are located i would take some of the fantastic windows out and replace them with French doors, or bi folding doors and connect the house to the site. The colour scheme from Karen is perfect to lift the kerb appeal and give it a modern twist. With land costing more than houses these days and the fact that you seem to have quite a big block, after looking at paint colours, opening up the living dining kitchen areas to the outside with a roofed area. Even combining a flat roofed carport which will widen the house to the street making it seem a bigger house, can carry the new look with say an enclosed section for garden equipment, to the opposite side to the house, and if you are lucky enough to have that near the living area it can be used as both car cover and outdoor living. I always think a good landscape architect is worth their weight in gold, to give you a landscape plan, to suit the soil type, your skills level and your preference in planting. Divide up the exterior space to provide outdoor rooms under a tree, paths that lead to some special spot for kids, maybe even a veggie patch with a chock run, and make sure that you use the entire yard, front and back by enclosing part of the front yard in fencing which suits the style of the house, while providing some planting to the street. If allowed a gate structure to blend in with the house, a dedicated pathway with planting each side to the front door, fantastic fencing and consider natural materials like a hand laid stone fence with timber or powder-coated aluminium inserts, to give this house an entry, not sure where the front door is now, so that is not a good look. Gardens always enhance a house, they are never a wasted effort, and if you are not gardeners, make sure the landscape architect knows that and he will be able to select low maintenance plants. All the paint in the world will not give the desired effort that the garden will do to that paint work.