--- a/gfx/src/nsColor.cpp
+++ b/gfx/src/nsColor.cpp
@@ -283,8 +283,20 @@ NS_HSL2RGB(float h, float s, float l)
     m2 = l + s - l*s;
   }
   m1 = l*2 - m2;
   r = uint8_t(255 * HSL_HueToRGB(m1, m2, h + 1.0f/3.0f));
   g = uint8_t(255 * HSL_HueToRGB(m1, m2, h));
   b = uint8_t(255 * HSL_HueToRGB(m1, m2, h - 1.0f/3.0f));
   return NS_RGB(r, g, b);  
 }
+
+NS_GFX_(const char*)
+NS_RGBToColorName(nscolor aColor)
+{
+  for (size_t idx = 0; idx < ArrayLength(kColors); ++idx) {
+    if (kColors[idx] == aColor) {
+      return kColorNames[idx];
+    }
+  }
+
+  return nullptr;
+}

--- a/gfx/src/nsColor.h
+++ b/gfx/src/nsColor.h
@@ -65,9 +65,16 @@ NS_GFX_(bool) NS_LooseHexToRGB(const nsS
 // Translate a color name to a color. Return true if it parses ok,
 // otherwise return false.
 NS_GFX_(bool) NS_ColorNameToRGB(const nsAString& aBuf, nscolor* aResult);
 
 // function to convert from HSL color space to RGB color space
 // the float parameters are all expected to be in the range 0-1
 NS_GFX_(nscolor) NS_HSL2RGB(float h, float s, float l);
 
+// Return a color name for the given nscolor.  If there is no color
+// name for it, returns null.  If there are multiple possible color
+// names for the given color, the first one in nsColorNameList.h
+// (which is generally the first one in alphabetical order) will be
+// returned.
+NS_GFX_(const char*) NS_RGBToColorName(nscolor aColor);
+
 #endif /* nsColor_h___ */

--- a/layout/inspector/public/inIDOMUtils.idl
+++ b/layout/inspector/public/inIDOMUtils.idl
@@ -52,16 +52,17 @@ interface inIDOMUtils : nsISupports
   const unsigned long INCLUDE_ALIASES = (1<<1);
   void getCSSPropertyNames([optional] in unsigned long aFlags,
 			   [optional] out unsigned long aCount,
 			   [retval, array, size_is(aCount)] out wstring aProps);
 
   // Utilities for working with CSS colors
   [implicit_jscontext]
   jsval colorNameToRGB(in DOMString aColorName);
+  AString rgbToColorName(in octet aR, in octet aG, in octet aB);
 
   // DOM Node utilities
   boolean isIgnorableWhitespace(in nsIDOMCharacterData aDataNode);
   // Returns the "parent" of a node.  The parent of a document node is the
   // frame/iframe containing that document.  aShowingAnonymousContent says
   // whether we are showing anonymous content.
   nsIDOMNode getParentForNode(in nsIDOMNode aNode,
                               in boolean aShowingAnonymousContent);

--- a/layout/inspector/src/inDOMUtils.cpp
+++ b/layout/inspector/src/inDOMUtils.cpp
@@ -432,16 +432,30 @@ inDOMUtils::ColorNameToRGB(const nsAStri
   if (!triple.ToObject(aCx, nullptr, aValue)) {
     return NS_ERROR_FAILURE;
   }
 
   return NS_OK;
 }
 
 NS_IMETHODIMP
+inDOMUtils::RgbToColorName(uint8_t aR, uint8_t aG, uint8_t aB,
+                           nsAString& aColorName)
+{
+  const char* color = NS_RGBToColorName(NS_RGB(aR, aG, aB));
+  if (!color) {
+    aColorName.Truncate();
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  aColorName.AssignASCII(color);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
 inDOMUtils::GetBindingURLs(nsIDOMElement *aElement, nsIArray **_retval)
 {
   NS_ENSURE_ARG_POINTER(aElement);
 
   *_retval = nullptr;
 
   nsCOMPtr<nsIMutableArray> urls = do_CreateInstance(NS_ARRAY_CONTRACTID);
   if (!urls)