Hi Brett about 5 to 10 years ago the trend was if your design style was contemporary your trim colour was the same as the walls and if your design style was classic your trim was a lighter, often white contrast to the wall colour. These days the trend is to the latter regardless of your design style as your builder's designers suggested. However matching your trim colour to the walls is still a good option if you have 8' ceilings. As there is minimal difference (only in the level of sheen) between the skirting boards and wall colour it makes the ceiling look higher. Another option is to do the trim in a similar but lighter tone such as Dulux Grey Pebble quarter. This is a very subtle tone on tone look. Whatever the colour, do you have a choice in the sheen level for your trim? I generally recommend semi gloss enamel on trim unless you are after a more classic look and your woodwork is in very good condition (the higher the sheen level the more any imperfections show up), in which case you could consider full gloss enamel. At the end of the day it's your home so you should do what you'd prefer - after all it's only paint so it's easily changed! All the best with your build.

@jmm1837, My appologies firstly to the author for being off topic. One house I lived in didn't have plaster anywhere, just pressboard for walls, the stuff notice boards are made from, so we wall papered as paint soaked in by the bucket load. then lived in a caravan and now a little relocatable cottage, a glorified caravan without wheels I say but now hubby and I are building our dream home, I have no decor or design education and have simply done my best with the plan and now the build. Great advice about making the home, warm, comfortable etc...and I'm doing what I want and not following trends BUT unfortunately at times I am truly paralized by indicision, too many choices of everything from interior colours to simple door handles and when I put my head down to sleep, my mind goes into overdrive, sleeping at times only a few hours a night ha-ha Still enjoying the process but it isn't that simple to follow your suggestions!!! I'm sure as the home progresses, with less decisions to make, it will become easier.

Whisper white is so very barely warm, I think it would achieve what you are after as it is often used in cool colour schemes. You can view the full range of Dulux whites on the attached link. If you click on a colour it will give you the break down of red, green, blue content for each colour. Just remember the colours on the screen will look different on your walls as the computer uses subtractive colour and you'll be painting with additive colour. http://www.dulux.com.au/specifier/colour/colour-atlas

Suggestions from neutral colours: https://www.dulux.com.au/colour/colour-trends/2018/essential Ceiling & walls the same colour is a good choice for square set. There will be subtle hue difference in various lighting situations anyway, which provides depth and makes for an interesting look.