ColorChooser : Improve plug alignment

This was broken slightly in GafferHQ#5902 when we introduced channel name
labels. The text width varies somewhat, causing the numeric widget and
sliders to be imperfectly aligned.

python/GafferUI/ColorChooser.py

@@ -162,19 +162,22 @@ def __init__( self, color=imath.Color3f( 1 ), **kw ) :
 
 		with self.__column :
 
-			# sliders and numeric widgets
-			for component in "rgbahsvtmi" :
-				with GafferUI.ListContainer( GafferUI.ListContainer.Orientation.Horizontal, spacing = 4 ) :
+			with GafferUI.GridContainer( spacing = 4 ) :
 
-					with GafferUI.ListContainer( GafferUI.ListContainer.Orientation.Horizontal, spacing = 8 ) :
-						GafferUI.Label( component.capitalize() )
-						numericWidget = GafferUI.NumericWidget( 0.0 )
+				# sliders and numeric widgets
+				for row, component in enumerate( "rgb_a_hsv_tmi" ) :
+					if component == "_" :
+						GafferUI.Spacer( imath.V2i( 0, 4 ), imath.V2i( 0, 4 ), parenting = { "index" : ( 0, row ) } )
+						continue
+
+					GafferUI.Label( component.capitalize(), parenting = { "index" : ( 0, row ), "alignment" : ( GafferUI.HorizontalAlignment.Center, GafferUI.VerticalAlignment.Center ) } )
+					numericWidget = GafferUI.NumericWidget( 0.0, parenting = { "index" : ( 1, row ) } )
 
 					numericWidget.setFixedCharacterWidth( 6 )
 					numericWidget.component = component
 					self.__numericWidgets[component] = numericWidget
 
-					slider = _ComponentSlider( color, component )
+					slider = _ComponentSlider( color, component, parenting = { "index" : ( 2, row ) } )
 					self.__sliders[component] = slider
 
 					self.__componentValueChangedConnections.append(
@@ -184,8 +187,6 @@ def __init__( self, color=imath.Color3f( 1 ), **kw ) :
 					self.__componentValueChangedConnections.append(
 						slider.valueChangedSignal().connect( Gaffer.WeakMethod( self.__componentValueChanged ), scoped = False )
 					)
-				if component in "bavi" :
-					GafferUI.Spacer( imath.V2i( 0, 4 ), imath.V2i( 0, 4 ) )
 
 			# initial and current colour swatches
 			with GafferUI.ListContainer( GafferUI.ListContainer.Orientation.Horizontal, spacing = 4 ) as self.__swatchRow :