I was prompted to re-read this after an absence of 3(cough) something years (good grief when did those years happen), by a discussion on 4 Mystery Addicts (the best online crime fiction discussion group that I've ever found).
Colour Scheme is one of Ngaio Marsh's books actually set in her homeland of New Zealand and was, I think, originally released in 1953 or 1943. Despite the age of the book it still holds up pretty well. There's a lovely underlying sense of humour about it, a bit too much stuffed shirt middle class English twit in some of the characters maybe, but there are two elements that stay with me.
Firstly landscape - the setting for the book is a hot springs / thermal area with a small residential hotel building. The smell of the sulphur and the bubbling of the mud along with the moonlike look were very evocative.
Secondly the inclusion of a number of characters from a local indigenious Maori group and their customs and beliefs was refreshing simply because they were just there. There was no particular over-statement of their existence, of their involvement or of their interactions. In other words, what I'm trying to say, is that no big deal was made of their presence.
The storyline itself interwove the involvement of all the characters well and the whole thing, whilst obviously written quite a while ago, was actually just an interesting book with a bit of a spy thriller sideline. Couple of minor silly things in the plot that were a little contrived but when you consider Marsh up against the more well-known Golden Age writers - she can hold her own pretty well.