Let param observer trigger grid color change

If you change the grid color in the preferences and cick the Apply button, the color of all grids is updated now. So you can experiment while the Preferences Editor is open.

I have kept but moved the grid color button in the Draft_SelectPlane task panel for now. So that both options can be tested.

src/Mod/Draft/Resources/ui/TaskSelectPlane.ui

@@ -153,6 +153,16 @@ will be moved to the center of the view</string>
    </item>
    <item>
     <layout class="QGridLayout" name="gridLayout">
+     <item row="0" column="0">
+      <widget class="QLabel" name="label_9">
+       <property name="text">
+        <string>Grid color</string>
+       </property>
+      </widget>
+     </item>
+     <item row="0" column="1">
+      <widget class="Gui::ColorButton" name="buttonColor"/>
+     </item>
      <item row="1" column="0">
       <widget class="QLabel" name="label_3">
        <property name="toolTip">
@@ -243,20 +253,6 @@ value by using the [ and ] keys while drawing</string>
      </property>
     </widget>
    </item>
-   <item>
-    <layout class="QGridLayout" name="gridLayout_4">
-     <item row="0" column="0">
-      <widget class="QLabel" name="label_9">
-       <property name="text">
-        <string>Grid color</string>
-       </property>
-      </widget>
-     </item>
-     <item row="0" column="1">
-      <widget class="Gui::ColorButton" name="buttonColor"/>
-     </item>
-    </layout>
-   </item>
    <item>
     <layout class="QGridLayout" name="gridLayout_3">
      <item row="0" column="0">

src/Mod/Draft/draftguitools/gui_selectplane.py

@@ -37,6 +37,7 @@ import WorkingPlane
 from FreeCAD import Units
 from drafttaskpanels import task_selectplane
 from draftutils import params
+from draftutils import utils
 from draftutils.messages import _msg
 from draftutils.todo import todo
 from draftutils.translate import translate
@@ -112,12 +113,9 @@ class Draft_SelectPlane:
         form.buttonPrevious.setIcon(QtGui.QIcon(":/icons/sel-back.svg"))
         form.buttonNext.setIcon(QtGui.QIcon(":/icons/sel-forward.svg"))
 
-        # color and transparency
+        # Grid color
         color = params.get_param("gridColor")
-        r = ((color >> 24) & 0xFF) / 255.0
-        g = ((color >> 16) & 0xFF) / 255.0
-        b = ((color >> 8) & 0xFF) / 255.0
-        form.buttonColor.setProperty("color", QtGui.QColor.fromRgbF(r, g, b))
+        form.buttonColor.setProperty("color", QtGui.QColor(utils.rgba_to_argb(color)))
 
         # Connect slots
         form.buttonTop.clicked.connect(self.on_click_top)
@@ -285,10 +283,8 @@ class Draft_SelectPlane:
             Gui.Snapper.showradius()
 
     def on_color_changed(self):
-        color = self.taskd.form.buttonColor.property("color").rgb() << 8
+        color = utils.argb_to_rgba(self.taskd.form.buttonColor.property("color").rgba())
         params.set_param("gridColor", color)
-        if self.grid is not None:
-            self.grid.update()
 
 Gui.addCommand('Draft_SelectPlane', Draft_SelectPlane())
 

src/Mod/Draft/draftguitools/gui_trackers.py

@@ -42,7 +42,6 @@ import FreeCAD
 import FreeCADGui
 import Draft
 import DraftVecUtils
-import WorkingPlane
 from FreeCAD import Vector
 from draftutils import params
 from draftutils import utils
@@ -1173,12 +1172,12 @@ class gridTracker(Tracker):
             self.coords3.point.setValues(apts)
             #self.lines3.numVertices.setValues(aidx)
             self.pts = pts
+
         # update the grid colors
         col, red, green, blue, gtrans = self.getGridColors()
         self.mat1.diffuseColor.setValue(col)
         self.mat2.diffuseColor.setValue(col)
         self.mat3.diffuseColor.setValues([col,red,green,blue])
-        self.setAxesColor()
 
     def getGridColors(self):
         """Returns grid colors stored in the preferences"""
@@ -1222,12 +1221,8 @@ class gridTracker(Tracker):
         self.coords_human.point.setValues(pts)
         self.human.numVertices.setValues(pidx)
 
-    def setAxesColor(self, wp=None):
+    def setAxesColor(self, wp):
         """set axes color"""
-        if not wp:
-            wp = getattr(FreeCAD, "DraftWorkingPlane", None)
-            if not wp:
-                wp = WorkingPlane.plane()
         cols = [0,0]
         if params.get_param("coloredGridAxes"):
             if round(wp.u.getAngle(FreeCAD.Vector(1,0,0)),2) in (0,3.14):