The upper House, or Legislative Council, is red, which reflects the colour of the House of Lords in the United Kingdom. Red represents nobility, as the nobles originally formed the membership of the House of Lords.
The House of Commons, or lower house, in the United Kingdom is green, representing the common people who are said to meet on grass.
It is not known why the Western Australian Legislative Assembly, or lower house, is blue. One theory is that the original furnishings from the Legislative Council, when it was located in the Perth CBD, were transferred to the new building on completion in 1904. The gold rush in Kalgoorlie and Coolgardie in the 1890s meant that the colony transitioned from being the poorest colony in Australia to one of the wealthiest, and there was a requirement to build infrastructure such as railways, Fremantle Harbour, the Supreme Court, the Parliament and the costly pipeline to Kalgoorlie. It is thought that perhaps there was not enough money left to furnish the new Legislative Assembly.