Revert "Core: Drop workarounds for IE <9"

This reverts commit fff7a1b.

It also updates README to mention details relevant for
jQuery Color 2.x.

Author: mgol

README.md

@@ -6,21 +6,19 @@ Supported jQuery versions: 1.5+
 
 ## Browser Support
 
-jQuery Color 3.x supports the following browsers:
+jQuery Color 2.x supports the following browsers:
 
 Desktop:
 * Chrome: (Current - 1) and Current
 * Edge: (Current - 1) and Current, 18
 * Firefox: (Current - 1) and Current, ESR
-* Internet Explorer: 9+
-* Safari: (Current - 1) and Current
+* Internet Explorer: 6+
+* Safari: 5.1+
 * Opera: Current
 
 Mobile:
-* Chrome on Android: (Current - 1) and Current
-* Safari on iOS: (Current - 2), (Current - 1) and Current
-
-Information on browser support of jQuery Color 2.x can be found in the [Browser Support section](https://github.com/jquery/jquery-color/blob/2.x-stable/README.md#browser-support) in its README.
+* Stock browser on Android 4.0+
+* Safari on iOS 7+
 
 ## Using jQuery Color in Production
 We release jQuery Color by itself, or in a bundle.  The extended names can be included as a jQuery Color plugin, or you can download the version of jQuery Color that includes the names.  Choose your build from the following list:

jquery.color.js

@@ -145,13 +145,21 @@
 			floor: true
 		}
 	},
+	support = color.support = {},
+
+	// element for support tests
+	supportElem = jQuery( "<p>" )[ 0 ],
 
 	// colors = jQuery.Color.names
 	colors,
 
 	// local aliases of functions called often
 	each = jQuery.each;
 
+// determine rgba support immediately
+supportElem.style.cssText = "background-color:rgba(1,1,1,.5)";
+support.rgba = supportElem.style.backgroundColor.indexOf( "rgba" ) > -1;
+
 // define cache name and alpha properties
 // for rgba and hsla spaces
 each( spaces, function( spaceName, space ) {
@@ -189,6 +197,12 @@ function clamp( value, prop, allowEmpty ) {
 	// ~~ is an short way of doing floor for positive numbers
 	value = type.floor ? ~~value : parseFloat( value );
 
+	// IE will pass in empty strings as value for alpha,
+	// which will hit this case
+	if ( isNaN( value ) ) {
+		return prop.def;
+	}
+
 	if ( type.mod ) {
 
 		// we add mod before modding to make sure that negatives values
@@ -446,7 +460,8 @@ color.fn = jQuery.extend( color.prototype, {
 		return "#" + jQuery.map( rgba, function( v ) {
 
 			// default to 0 when nulls exist
-			return ( "0" + ( v || 0 ).toString( 16 ) ).substr( -2 );
+			v = ( v || 0 ).toString( 16 );
+			return v.length === 1 ? "0" + v : v;
 		} ).join( "" );
 	},
 	toString: function() {
@@ -617,13 +632,36 @@ color.hook = function( hook ) {
 	each( hooks, function( _i, hook ) {
 		jQuery.cssHooks[ hook ] = {
 			set: function( elem, value ) {
-				var parsed;
+				var parsed, curElem,
+					backgroundColor = "";
 
 				if ( value !== "transparent" && ( getType( value ) !== "string" || ( parsed = stringParse( value ) ) ) ) {
 					value = color( parsed || value );
+					if ( !support.rgba && value._rgba[ 3 ] !== 1 ) {
+						curElem = hook === "backgroundColor" ? elem.parentNode : elem;
+						while (
+							(backgroundColor === "" || backgroundColor === "transparent") &&
+							curElem && curElem.style
+						) {
+							try {
+								backgroundColor = jQuery.css( curElem, "backgroundColor" );
+								curElem = curElem.parentNode;
+							} catch ( e ) {
+							}
+						}
+
+						value = value.blend( backgroundColor && backgroundColor !== "transparent" ?
+							backgroundColor :
+							"_default" );
+					}
+
 					value = value.toRgbaString();
 				}
-				elem.style[ hook ] = value;
+				try {
+					elem.style[ hook ] = value;
+				} catch( e ) {
+					// wrapped to prevent IE from throwing errors on "invalid" values like 'auto' or 'inherit'
+				}
 			}
 		};
 		jQuery.fx.step[ hook ] = function( fx ) {