Scientists are smart - the way they figured this out is really clever, because they literally "blinded" the participants to the study; they're not asking you to tell them what color comes to mind, they ask you to just choose the neutral gray. This is how they figure out racial bias too:
Our sense of smell alters the colors we see, show scientists
Oct 2023, phys.org
"In a previous study, we had shown that the odor of caramel commonly constitutes a crossmodal association with dark brown and yellow, just like coffee with dark brown and red, cherry with pink, red, and purple, peppermint with green and blue, and lemon with yellow, green, and pink," explained Ward.Ward and colleagues tested 24 adult women and men between 20 and 57 years of age with one of six odors chosen at random from caramel, cherry, coffee, lemon, and peppermint, plus odorless water as a control, and asked to manually adjust two sliders - one for yellow to blue, and another for green to red - to change its color to neutral gray.Participants had a weak but significant tendency to adjust one or both of the sliders too far away from neutral gray. For example, when presented with the odor of coffee, they wrongly perceived 'gray' to be more of a red-brown color than true neutral gray.An exception was when the odor of peppermint was presented: here, the participants' choice of hue was different from the typical crossmodal association demonstrated for the other odors. As expected, the participants' selection likewise corresponded to true gray when presented with the neutral scent of water.
via John Moores University in Liverpool: Ryan J. Ward et al, Odors modulate color appearance, Frontiers in Psychology (2023). DOI: 10.3389/fpsyg.2023.1175703
Image credit: AI Art - Face of Quasiparticles - 2023