Walk down any grocery aisle or scroll through an online marketplace, and you’re making snap judgments about product size without realizing it. A bottle looks generous or stingy. A suitcase looks roomy or cramped. A sofa looks like it will fill the living room or get swallowed by it. Marketers have long known that these perceptions shape what we buy, and they’ve studied plenty of visual tricks that nudge our estimates up or down. But one everyday factor has gone relatively unexamined: the color relationship between a product and the background it sits against.
New research published in Psychology & Marketing takes on that gap. Across five studies and two supplementary experiments, the authors found that when a product’s color contrasts sharply with its background, shoppers perceive the product as bigger than the same product shown against a background of a similar hue.
The question behind the research
Yanzheng Liu of Renmin University of China and Chen Yang of Jimei University set out to answer a question that prior work had largely sidestepped. Researchers have examined how product shape, movement speed, image format (2D versus 3D), and even how products are spaced on a shelf affect size perception. Color had mostly been studied in terms of saturation, meaning how vivid or muted a single color appears. What happens when you combine two colors, one on the product and one behind it, was less understood.
The authors focused on what’s called hue-based contrast. Picture a color wheel. Colors that sit next to each other (yellow and yellow-orange, for instance) produce low contrast, while colors on opposite sides of the wheel (yellow and blue) produce high contrast. The researchers wanted to know whether that relationship between product and background shifts how large a product appears and, if so, why.
What the studies tested
The team ran participants through a sequence of experiments using different products, including watches, sofas, suitcases, and mouthwashes, with product colors ranging across blue, brown, silver, orange, and yellow. In each case, participants viewed an image of a product against either a high-contrast or low-contrast background and then estimated the product’s size, sometimes using a slider scale calibrated to real-world measurements (for example, 25 to 40 millimeters for a watch dial, or 0.4 to 3.0 square meters for a sofa).
In the first study, 260 participants saw a brown watch either against a yellow background (high contrast) or a brown background (low contrast). Those who saw the high-contrast version estimated the dial at about 33.25 millimeters on average, while the low-contrast group estimated 32.31 millimeters. A small difference, but a statistically reliable one.
A second study with 400 participants tackled a potential confound. Because contrast can be adjusted by changing saturation rather than hue, it was possible that the size effect was really a saturation effect. The researchers separated the two, varying product saturation and product-background contrast independently. The contrast effect held regardless of saturation: higher contrast produced larger size estimates whether the product was vividly colored or muted.
Why the effect happens
A third study, with 200 participants viewing suitcase images, examined the psychological chain of events behind the effect. The authors proposed a two-step process. First, high contrast makes the edges of a product stand out more clearly against its surroundings, what they call visual boundary clarity. Second, clearer edges make it easier for the brain to process the product’s shape, a phenomenon known as processing fluency, meaning the subjective sense that something is easy to perceive.
The data lined up with that sequence. Participants who saw the high-contrast suitcase rated its visual boundary as sharper, reported that estimating the size felt easier, and judged the suitcase as larger. The researchers also checked whether the effect might be explained by other factors: did the high-contrast version just look more attractive, more unique, higher quality, or more premium? None of those alternatives accounted for the size difference.
The authors interpret the pattern this way: when visual information feels easy to process, people seem to read that ease as a signal that the object is substantial or spatially prominent, and they adjust their size estimates upward.
When the effect disappears
The fourth study introduced a boundary condition. If the mechanism really runs through boundary clarity and processing fluency, then anything that muddles boundary perception should weaken the effect. Background complexity was a natural candidate.
With 400 participants viewing sofas, the researchers varied both contrast and background complexity. In the simple-background condition, the sofa appeared against a plain colored wall. In the complex condition, the background included a lamp, wall art, and other decorative elements. When the background was simple, high contrast again produced larger size estimates than low contrast. When the background was cluttered, the contrast advantage vanished. Sofas in both contrast conditions were judged to be about the same size.
A supplementary study found a similar weakening when participants had more prior knowledge about the product category. Novice shoppers responded strongly to the contrast cue; more experienced ones were less swayed by it.
Does any of this change what people buy?
A final study with 400 participants connected the size perception effect to purchase intentions. Participants were asked to imagine shopping for mouthwash, either a small, portable bottle for occasional use or a large bottle for frequent use. They then saw an orange mouthwash displayed against either a yellow (low-contrast) or blue (high-contrast) background.
When participants wanted a larger bottle, they reported higher purchase intentions for the high-contrast display. When they wanted a smaller, portable bottle, the pattern flipped: the low-contrast display drew more interest. The visual presentation that best matched the shopper’s size goal won out.
Practical takeaways and caveats
For marketers, the authors suggest that product-background color contrast is a low-cost lever. Sharpening the contrast between a product and its backdrop in ads, packaging, or e-commerce images can push perceived size upward, which is useful when shoppers are looking for a generous, full-featured product. Softer contrast may serve products being marketed as compact or travel-friendly. Either way, the researchers argue, the visual presentation should match the size attribute that matters to the target buyer.
Several caveats come with the findings. Most of the experiments used two-color combinations against plain backgrounds, which isolates the contrast effect but doesn’t capture the visual clutter of a real store shelf or a busy webpage. The authors note there’s no established formula for calculating overall perceived contrast in multicolored, complex scenes. The studies also relied on static, online images; lighting, motion, and in-person shopping contexts could interact with contrast in ways this research didn’t test. Age-related changes in vision and cross-cultural differences in color preferences are also open questions.
The authors close with an ethical note: visual strategies that shift size perceptions are legitimate marketing tools, but they can shade into misleading territory if a product’s appearance diverges too far from its actual dimensions.
