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Some earlier studies had found no clear color preference among mosquitoes. One study found they prefer blue, another that they prefer yellow-green. What should people make of such conflicting results?

The apparent color of an object doesn’t just depend on the wavelengths of light it gives off, Claire Rusch explains, who studies mosquitoes for years. It also can be affected by the brightness of that light and its contrast against surrounding colors. Humans see an object’s color largely in terms of the wavelengths of light it gives off. But other creatures’ eyes may be more sensitive to contrast or brightness. “We needed to control all of those variables to really be sure a mosquito’s preferences came from the wavelength of the object,” Rusch says.

To do this, she designed a test chamber (室) that was 450 mosquito-body-lengths long in her experiment. Lined with cameras, it recorded the insects’ flight patterns. Two small colored disks laid on the floor of the chamber.

Since the researchers wanted to know if mosquitoes were attracted to certain colors, the disks couldn't be the darkest or brightest objects in the chamber. Otherwise, it would be unclear if the mosquitoes were attracted to the disks’ color, contrast or brightness. So, the researchers projected a chessboard pattern onto the floor of the chamber and gray along the walls. That way, if the mosquitoes went to the colored disks, it could only be due to the disks’ color.

The researchers released about 50 starved mosquitoes into the chamber at a time. Because mosquitoes don't start hunting until they’ve sensed CO₂, so the team sprayed (喷) CO₂ inside the chamber. They found before CO₂ was sprayed, the mosquitoes ignored all the colored disks. With CO₂, mosquitoes ignored any disk that was green, blue or purple. But the insects did fly toward disks that were red, orange or light blue. They seemed to especially like red.

To further investigate that, the team placed disks with different skin tones. But the mosquitoes didn't seem to prefer any particular skin colors. All were equally attractive.