SeleniumHQ/selenium · error · ArgumentError

could not convert #{str.inspect} into color

Error message

could not convert #{str.inspect} into color

What it means

Support::Color.from_string parses a CSS color string by trying a fixed set of regexes (rgb, rgb%, rgba, rgba%, #rrggbb, #rgb, hsl, hsla). If none match it raises ArgumentError. Crucially, CSS named colors ('red', 'blue', 'transparent') and modern syntaxes (space-separated rgb(), 8-digit hex, color()) are NOT supported by these patterns, so a visually-valid color string can still fail.

Source

Thrown at rb/lib/selenium/webdriver/support/color.rb:71

            new Regexp.last_match(1), Regexp.last_match(2), Regexp.last_match(3)
          when RGB_PCT_PATTERN
            array = [Regexp.last_match(1), Regexp.last_match(2), Regexp.last_match(3)]
            new(*array.map { |e| Float(e) / 100 * 255 })
          when RGBA_PATTERN
            new Regexp.last_match(1), Regexp.last_match(2), Regexp.last_match(3), Regexp.last_match(4)
          when RGBA_PCT_PATTERN
            array = [Regexp.last_match(1), Regexp.last_match(2), Regexp.last_match(3)]
            new(*array.map { |e| Float(e) / 100 * 255 } << Regexp.last_match(4))
          when HEX_PATTERN
            array = [Regexp.last_match(1), Regexp.last_match(2), Regexp.last_match(3)]
            new(*array.map { |e| e.to_i(16) })
          when HEX3_PATTERN
            array = [Regexp.last_match(1), Regexp.last_match(2), Regexp.last_match(3)]
            new(*array.map { |e| (e * 2).to_i(16) })
          when HSL_PATTERN, HSLA_PATTERN
            from_hsl(Regexp.last_match(1), Regexp.last_match(2), Regexp.last_match(3), Regexp.last_match(4))
          else
            raise ArgumentError, "could not convert #{str.inspect} into color"
          end
        end

        def self.from_hsl(hue, sat, light, alpha)
          hue = Float(hue) / 360
          sat = Float(sat) / 100
          light = Float(light) / 100
          alpha = Float(alpha || 1)

          if sat.zero?
            r = light
            g = r
            b = r
          else
            luminocity2 = light < 0.5 ? light * (sat + 1) : light + sat - (light * sat)
            luminocity1 = (light * 2) - luminocity2

            r = hue_to_rgb(luminocity1, luminocity2, hue + (1.0 / 3.0))

View on GitHub (pinned to aa36b38e69)

Solutions

1. Normalize the string to a supported format (comma-separated rgb()/rgba()/hsl()/hsla() or #rrggbb) before calling from_string.
2. If the value came from getCssValue, convert space-separated rgb(r g b / a) to comma form rgba(r, g, b, a).
3. Map named colors to hex yourself before parsing, since from_string does not recognize color names.

Example fix

# before (browser may return space-separated form)
color = Selenium::WebDriver::Support::Color.from_string(element.css_value('background-color'))

# after
raw = element.css_value('background-color')
raw = raw.sub(/rgba?\(([^)]+)\)/) { |inner| "rgba(#{inner.tr(' /', ', ')})" }
color = Selenium::WebDriver::Support::Color.from_string(raw)

SUPPORTED_COLOR = /^\s*(rgb|rgba|hsl|hsla)\(|#\h{3}(?:\h{3})?\b/

def parseable_color?(str)
  str.is_a?(String) && str.match?(SUPPORTED_COLOR)
end

color = parseable_color?(raw) ? Color.from_string(raw) : fallback

def legacy_css_color?(str)
  return false unless str.is_a?(String)
  patterns = [Color::RGB_PATTERN, Color::RGBA_PATTERN, Color::HEX_PATTERN,
              Color::HEX3_PATTERN, Color::HSL_PATTERN, Color::HSLA_PATTERN]
  patterns.any? { |p| str.match?(p) }
end

begin
  Color.from_string(raw)
rescue ArgumentError => e
  raise unless e.message.include?('into color')
  Color.from_string(normalize_to_legacy_rgb(raw))
end

When it happens

Trigger: Calling Selenium::WebDriver::Support::Color.from_string with a named color ('red'), a modern css4 color function (color(srgb 1 0 0)), an 8-digit hex (#ff0000ff), a space-separated rgb (rgb(255 0 0)), a malformed/empty string, or a value with surrounding markup. Only the legacy comma-delimited rgb()/rgba()/hsl()/hsla() and #rgb/#rrggbb forms parse.

Common situations: Reading element.style.color or getCssValue('color') and passing it through Color.from_string; browsers increasingly return the space-separated rgb() form for getCssValue, which does not match RGBA_PATTERN and fails; test data with named colors.

Related errors

• Did not know how to convert ${value} into color
• Safari does not support options that are not namespaced
• unexpected tag name #{tag_name.inspect}
• Could not convert {str_} into color
• name is required

AI-assisted analysis of SeleniumHQ/selenium@aa36b38e69 (2026-08-14). Data as JSON: /api/errors/ef856c891309e60a. Report an issue: GitHub.