The Visual Relationships Born from Contrast & Similarity
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• Cool Colors – Greens, blues, purples. These lean closer towards relaxing, calming, subduing, and passivity. How can you use this to your advantage? It’s simple if you know one easy rule: warm colors tend to dominate cool colors. For example, making a call-to-action button red can help attract attention to it, but setting that red call-to-action button against a blue or green background will draw even more attention.
See how clearly yellow stands out over the blue in the above example? Likewise, the red takes the attention from the green, almost shrinking it.
Source: TV Safety.org