Just a quicky: I have published a preferences file for Archi that you can load to get the 9-colour scheme that is use in my book. See the book main page for a link to the preferences file. If you use it, the default object colouring is like this (example):
ArchiMate is officially colour-neutral. Historically, blue was used for active structural elements, yellow for their behaviour and green for the passive structural elements the behaviour worked with. Later a yellow/blue/green colour scheme for business/application/infrastructure was introduced. You will find both colour schemes in the official standard, though the original colour scheme is used for metamodel explanations and the later scheme for the examples. If you are interested in the how and why of my colour scheme (which uses the original scheme but adapted such that you can also differentiate between business, application, and infrastructure), see the book, but in summary: the column-division of colouring makes views that are single-layer much easier to digest (it is far easier to quickly determine ‘actors’ and ‘behaviour’, etc.). The slight differences in colour intensity also makes multi-layer views easier to read.
The Archi colour preferences file is part of the Mastering ArchiMate Tool Support distribution. It can be found at the bottom of the home page for the book or via this link.