Yellow was a very popular colour in the 1960s and 1970s.
If you watch old films you'll be familiar with seeing homes from the 1940s and 1950s and they were austere - full of dark, plain colours and traditional materials. The 1940s/50s were times of great uncertainty, fear and economic hardship for many people and the dark, restrained, often gloomy homes reflected this. Young people dressed more or less as their parents had and homes changed little as they passed from one generation to the next.
By contrast the 1960s were a time of great hope, enthusiasm and optimism about the future. Many people were enjoying increased disposable income and leisure time and they wanted to spend some of this time and money on beautifying their homes.
They were also times of new fashions, music, social attitudes - times of experimentation and expressing ones individuality. And technological advances brought new materials, especially plastic, and new techniques that facilitated bright colours and products at much lower cost than before.
There was a consumer boom in the 1960s and those consumers loved bright colours and new shiny materials that expressed the excitement and hope they felt.