[DOCs][PCB Print] Added remainder about alpha channel

See #531

docs/samples/generic_plot.kibot.yaml

@@ -2296,7 +2296,8 @@ outputs:
           # Order is important, the last goes on top.
           # You can reuse other layers lists, some options aren't used here, but they are valid
           layers:
-            # [string=''] Color used for this layer
+            # [string=''] Color used for this layer.
+            # KiCad 6+: don't forget the alpha channel for layers like the solder mask
             - color: ''
               # [string=''] A description for the layer, for documentation purposes.
               # A default can be specified using the `layer_defaults` global option
@@ -2333,7 +2334,8 @@ outputs:
           # [list(dict)|list(string)|string] List of layers to replace `repeat_for_layer`.
           # This can be used to generate a page for each copper layer, here you put `copper`
           repeat_layers:
-            # [string=''] Color used for this layer
+            # [string=''] Color used for this layer.
+            # KiCad 6+: don't forget the alpha channel for layers like the solder mask
             - color: ''
               # [string=''] A description for the layer, for documentation purposes.
               # A default can be specified using the `layer_defaults` global option

docs/source/configuration/outputs/pcb_print.rst

@@ -46,6 +46,7 @@ Parameters:
                -  Valid keys:
 
                   -  ``color`` :index:`: <pair: output - pcb_print - options - pages - layers; color>` [string=''] Color used for this layer.
+                     KiCad 6+: don't forget the alpha channel for layers like the solder mask.
                   -  ``description`` :index:`: <pair: output - pcb_print - options - pages - layers; description>` [string=''] A description for the layer, for documentation purposes.
                      A default can be specified using the `layer_defaults` global option.
                   -  ``force_plot_invisible_refs_vals`` :index:`: <pair: output - pcb_print - options - pages - layers; force_plot_invisible_refs_vals>` [boolean=false] Include references and values even when they are marked as invisible.
@@ -79,6 +80,7 @@ Parameters:
                -  Valid keys:
 
                   -  ``color`` :index:`: <pair: output - pcb_print - options - pages - repeat_layers; color>` [string=''] Color used for this layer.
+                     KiCad 6+: don't forget the alpha channel for layers like the solder mask.
                   -  ``description`` :index:`: <pair: output - pcb_print - options - pages - repeat_layers; description>` [string=''] A description for the layer, for documentation purposes.
                      A default can be specified using the `layer_defaults` global option.
                   -  ``force_plot_invisible_refs_vals`` :index:`: <pair: output - pcb_print - options - pages - repeat_layers; force_plot_invisible_refs_vals>` [boolean=false] Include references and values even when they are marked as invisible.

kibot/out_pcb_print.py

@@ -138,7 +138,8 @@ class LayerOptions(Layer):
         self._unknown_is_error = True
         with document:
             self.color = ""
-            """ Color used for this layer """
+            """ Color used for this layer.
+                KiCad 6+: don't forget the alpha channel for layers like the solder mask """
             self.plot_footprint_refs = True
             """ Include the footprint references """
             self.plot_footprint_values = True