Warm or cool color checker by hue angle

Red at 0 degrees is the warm center, cyan at 180 degrees is the cool center, and the nearer center determines the result. Exact boundary hues are classified as cool for a stable tie rule. The response includes the normalized color, hue, category, and angular distance, making the decision transparent and repeatable in design tools, tests, and automated color workflows.

How the warm and cool decision is made

This checker uses a geometric definition on the standard RGB hue circle. Red, at 0 degrees, is the center of the warm half; cyan, at 180 degrees, is the center of the cool half. After converting the supplied hexadecimal color to a hue, the calculator measures the shortest angular distance to the warm center. A distance below 90 degrees produces warm, while a distance of 90 degrees or more produces cool. The two dividing hues are therefore 90 and 270 degrees. Because those positions are equally distant from the two centers, the calculator assigns both exact ties to cool. That explicit tie rule prevents different applications from making different choices at a boundary. The output reports the hue and distance used in the decision, so the category is auditable rather than a hidden opinion. This classification is a practical digital-color convention; visual warmth can still shift with surrounding colors, lighting, and cultural context.

Entering a color and reading the result

Enter one hexadecimal RGB color using either the three-digit form, such as #F60, or the six-digit form, such as #FF6600. The leading hash is optional, and letter case does not matter. The response expands shorthand and returns an uppercase six-digit value in the color field. The hue_degrees field gives the calculated position from 0 up to, but not including, 360 degrees. Category is the requested warm or cool label. Distance_from_warm_center shows how far the hue lies from red along the shorter route around the circle, while the two center fields state the reference angles used by the rule. A result near a 90-degree distance is close to the divide and may look context-sensitive even though the computational answer remains stable. Black, white, and every exact gray are rejected: their red, green, and blue channels are equal, so hue is mathematically undefined and a hue-based warm/cool label would be fabricated.

Using deterministic temperature labels in a workflow

A deterministic label is useful when a palette must be filtered, tested, or routed without a person making the same judgment repeatedly. A design-system script can classify candidate accent colors and verify that a warm collection contains only warm results. A catalog pipeline can add a searchable temperature facet to chromatic product swatches. A chart generator can select a contrasting family by checking the category before it chooses supporting colors. The calculation has no network calls, random choices, stored state, or current-time dependency, so identical input always produces identical output. For automation through the API, each request costs $0.002; the browser runner uses the same pure calculation. Treat the label as one measurable property rather than a complete theory of color appearance. Saturation and lightness do not move the hue angle, but they strongly affect how confidently people perceive warmth. For nuanced art direction, review the classified color beside its intended background and neighboring palette after using this result as a consistent first pass.