Update ColorPalette component to accept disableAlpha parameter (#18175)

* Add disableAlpha parameter to ColorPalette

Adds the disableAlpha parameter to ColorPalette component which is
passed forward to the ColorPicker to show. Previously it was set to true
by default. Fixes #4726

* Update documentation with disableAlpha parameter

packages/components/src/color-palette/README.md

@@ -50,6 +50,14 @@ Whether the palette should have a clearing button or not.
 - Required: No
 - Default: true
 
+### disableAlpha
+
+Whether to disable alpha channel controls or not.
+
+- Type: `Boolean`
+- Required: No
+- Default: true
+
 
 ## Usage
 ```jsx

packages/components/src/color-palette/index.js

@@ -19,6 +19,7 @@ export default function ColorPalette( {
 	clearable = true,
 	className,
 	colors,
+	disableAlpha = true,
 	disableCustomColors = false,
 	onChange,
 	value,
@@ -55,7 +56,7 @@ export default function ColorPalette( {
 			<ColorPicker
 				color={ value }
 				onChangeComplete={ ( color ) => onChange( color.hex ) }
-				disableAlpha
+				disableAlpha={ disableAlpha }
 			/>
 		),
 		[ value ]

packages/components/src/color-palette/stories/index.js

@@ -54,3 +54,17 @@ export const withKnobs = () => {
 	);
 };
 
+export const withAlpha = () => {
+	const colors = [
+		object( 'Red', { name: 'red', color: '#f00' } ),
+		object( 'White', { name: 'white', color: '#fff' } ),
+		object( 'Blue', { name: 'blue', color: '#00f' } ),
+	];
+
+	return (
+		<ColorPaletteWithState
+			colors={ colors }
+			disableAlpha={ false }
+		/>
+	);
+};