Where these names come from
CSS, the language that styles web pages, defines a fixed set of color keywords. Most came from the old X11 window system's color list and were standardized in CSS Color Module Level 3. Level 4 added rebeccapurple in 2014, in memory of Rebecca Meyer, the daughter of CSS pioneer Eric Meyer. You can write color: tomato instead of color: #FF6347 and every browser shows the same color.
A few quirks are worth knowing:
darkgray(#A9A9A9) is lighter thangray(#808080), a leftover from the two lists the names were merged from.- Every keyword spelled "gray" also accepts "grey", for example
slategrey. aquaandcyanare the same color, and so arefuchsiaandmagenta.
Using a code
Copy the HEX from any swatch and use it anywhere colors are accepted: CSS, design apps, Office documents, game editors. The "Aa" figure on each swatch is the contrast ratio of the better text color, black or white, on that background. 4.5:1 or more meets WCAG AA for normal text.
Beyond the keyword list
The keywords are a convenient shorthand, not a palette. Many are dated (papayawhip, blanchedalmond) and the jumps between them are uneven. For a design, pick a family page above for curated shades, or start from one color in the hex color picker and build a set with the color palette generator. To translate a code into RGB, HSL or OKLCH, use the color converter, and to name any code you find, try the color name finder.