Color Brightness Skill

Overview

Color Brightness Calculator works by applying WCAG 2.0 relative luminance formulas to RGB color values, calculating contrast ratios with black and white, and determining optimal text colors for accessibility.

Live Test Color Brightness Skill Skill →

The tool

Once your client is connected to the VerveKit server, this appears in its tool list as ColorBrightnessSkill. It is read-only and open-world — it fetches and never mutates anything on your side — so most clients call it without asking you to confirm.

Tool call

{
  "name": "ColorBrightnessSkill",
  "arguments": {
    "hex": "FF5733"
  }
}

You do not name the tool yourself; the model picks it. Asking about FF5733 in the terms this skill covers is enough for it to reach for ColorBrightnessSkill on its own — naming it explicitly also works, and is the way to force the call.

Connecting

One server URL covers every skill in the catalog, including this one. Authorization is OAuth: the client opens a browser once, and there is no key to paste into a config file.

{
  "mcpServers": {
    "vervekit": {
      "url": "https://api.vervekit.com/v1/mcp"
    }
  }
}

Per-client setup — Claude, Cursor, VS Code, ChatGPT — is on the MCP setup page.

Arguments

These are the properties on the tool's inputSchema, so a well-behaved client validates them before the call is made. Premium arguments are accepted on every plan but only take effect on plans that include them.

Argument	Type	Description
`hex`Required	string	Hex color value (with or without # prefix) hexColor

What the model gets back

The result carries a structuredContent object matching the tool's declared outputSchema, so a client reads fields without parsing prose. status is "ok" and error is null on success; a null field means the value was not available for that input, not that the call failed.

Result

{
  "status": "ok",
  "error": null,
  "data": {
    "hex": "#FF5733",
    "rgb": {
      "r": 255,
      "g": 87,
      "b": 51
    },
    "luminance": 0.2832,
    "perceived_brightness": 131,
    "yiq": 133.13,
    "is_light": false,
    "is_dark": true,
    "brightness_category": "dark",
    "recommended_text_color": "#FFFFFF",
    "contrast_ratio_with_white": 3.15,
    "contrast_ratio_with_black": 6.66,
    "wcag_aa_compliant_with_white": false,
    "wcag_aa_compliant_with_black": true,
    "wcag_aaa_compliant_with_white": false,
    "wcag_aaa_compliant_with_black": false
  }
}

Response fields

Paths are relative to data. Premium fields are absent rather than zeroed on plans that do not include them, so check for presence instead of comparing to 0.

Field	Type	Example	Description
`hex`	string	`#FF5733`	Hexadecimal color value provided in the request
`rgb`	object	`{…}`	RGB color components: red, green, blue values
`rgb.r`	number	`255`	Red component value between 0 and 255
`rgb.g`	number	`87`	Green component value between 0 and 255
`rgb.b`	number	`51`	Blue component value between 0 and 255
`luminance`Premium	number	`0.2832`	Relative luminance calculated using WCAG 2.0 formula
`perceived_brightness`Premium	number	`131`	Perceived brightness score from 0 to 255
`yiq`Premium	number	`133.13`	YIQ color space brightness value for brightness analysis
`is_light`	boolean	`false`	Boolean indicating if color is considered light
`is_dark`	boolean	`true`	Boolean indicating if color is considered dark
`brightness_category`	string	`dark`	Brightness classification: light, medium, or dark category
`recommended_text_color`Premium	string	`#FFFFFF`	Recommended text color for optimal contrast and readability
`contrast_ratio_with_white`Premium	number	`3.15`	WCAG contrast ratio calculation between color and white
`contrast_ratio_with_black`Premium	number	`6.66`	WCAG contrast ratio calculation between color and black
`wcag_aa_compliant_with_white`Premium	boolean	`false`	Whether color meets WCAG AA contrast requirements with white
`wcag_aa_compliant_with_black`Premium	boolean	`true`	Whether color meets WCAG AA contrast requirements with black
`wcag_aaa_compliant_with_white`Premium	boolean	`false`	Whether color meets WCAG AAA contrast requirements with white
`wcag_aaa_compliant_with_black`Premium	boolean	`false`	Whether color meets WCAG AAA contrast requirements with black

Failure modes

Errors come back as tool errors carrying a sentence the model can act on, not a bare status code. Error handling covers the full list.

Status	What it means
`400` / `422`	The arguments did not validate. The message names the offending one.
`401`	The OAuth session is invalid or expired — reconnect the server.
`403`	Blocked by a key restriction or an IP allow-list. Never a bad identity.
`404`	This skill is not part of VerveKit. Check the catalog.
`429`	Out of credits, or a brief rate limit. The message tells them apart.

A call costs 2 credits each time the tool actually runs; a model that reasons about the tool without calling it costs nothing.

Use cases

Web Accessibility: Ensure WCAG compliance by calculating contrast ratios for text and background colors
UI Design: Determine appropriate text colors for backgrounds based on brightness calculations
Theme Development: Automatically select light or dark text based on background color brightness
Color Analysis: Analyze color brightness and categorize colors for design systems and palettes

Other ways to use Color Brightness Skill

Set up Color Brightness Skill on VerveKit, or reach the same source a different way. Your VerveKit account and credits work on all of them — one key, one balance.

Call it as a REST APIOne HTTPS endpoint and an x-api-key header, with SDKs for Node, Python and .NET.APIVerve →Reference →

Google Sheets or ExcelA =VERVE() formula fills a column — no script, no export, recalculates in place.VerveSheets →Reference →

Ground an agent on itA cited, machine-checkable fact your model can't produce on its own.VerveContext →Reference →