Which of the following factors does NOT influence price elasticity of demand?

The correct answer identifies that the color of the packaging of a good does not influence its price elasticity of demand. Price elasticity of demand measures how sensitive the quantity demanded of a good is to a change in its price.

The other choices listed—availability of substitutes, the necessity versus luxury nature of the good, and the proportion of income spent on the good—are all significant factors. When substitutes are readily available, consumers can easily switch if the price rises, leading to higher elasticity. Similarly, goods considered necessities tend to have lower elasticity because consumers need to purchase them regardless of price changes, while luxury items can often see a greater drop in demand as prices increase. Lastly, if a substantial portion of a consumer's income is spent on a good, a price increase may lead to more noticeable reductions in quantity demanded, reflecting higher elasticity.

In contrast, the color of the packaging is largely a marketing choice that does not fundamentally alter the economic relationship between price and the quantity demanded. While it may affect consumer perception or brand loyalty, it does not directly influence the demand's responsiveness to price changes.