+
+ def colour_preview(key, value)
+ return nil unless key =~ /^(?>.+:)?colour$/ && !value.nil? # see discussion at https://github.com/openstreetmap/openstreetmap-website/pull/1779
+
+ # does value look like a colour? ( 3 or 6 digit hex code or w3c colour name)
+ w3c_colors =
+ %w[aliceblue antiquewhite aqua aquamarine azure beige bisque black blanchedalmond blue blueviolet brown burlywood cadetblue chartreuse chocolate
+ coral cornflowerblue cornsilk crimson cyan darkblue darkcyan darkgoldenrod darkgray darkgrey darkgreen darkkhaki darkmagenta darkolivegreen
+ darkorange darkorchid darkred darksalmon darkseagreen darkslateblue darkslategray darkslategrey darkturquoise darkviolet deeppink deepskyblue
+ dimgray dimgrey dodgerblue firebrick floralwhite forestgreen fuchsia gainsboro ghostwhite gold goldenrod gray grey green greenyellow honeydew
+ hotpink indianred indigo ivory khaki lavender lavenderblush lawngreen lemonchiffon lightblue lightcoral lightcyan lightgoldenrodyellow lightgray
+ lightgrey lightgreen lightpink lightsalmon lightseagreen lightskyblue lightslategray lightslategrey lightsteelblue lightyellow lime limegreen
+ linen magenta maroon mediumaquamarine mediumblue mediumorchid mediumpurple mediumseagreen mediumslateblue mediumspringgreen mediumturquoise
+ mediumvioletred midnightblue mintcream mistyrose moccasin navajowhite navy oldlace olive olivedrab orange orangered orchid palegoldenrod
+ palegreen paleturquoise palevioletred papayawhip peachpuff peru pink plum powderblue purple red rosybrown royalblue saddlebrown salmon
+ sandybrown seagreen seashell sienna silver skyblue slateblue slategray slategrey snow springgreen steelblue tan teal thistle tomato turquoise
+ violet wheat white whitesmoke yellow yellowgreen]
+ return nil unless value =~ /^#([0-9a-fA-F]{3}){1,2}$/ || w3c_colors.include?(value.downcase)
+
+ value
+ end