diff --git a/pcbnew/board_stackup_manager/stackup_predefined_prms.cpp b/pcbnew/board_stackup_manager/stackup_predefined_prms.cpp
index 950d5fb49a..bbe473ceb6 100644
--- a/pcbnew/board_stackup_manager/stackup_predefined_prms.cpp
+++ b/pcbnew/board_stackup_manager/stackup_predefined_prms.cpp
@@ -61,7 +61,8 @@ static wxString CopperFinishType[] =
 // A list of available colors for solder mask and silkscreen
 // These names are used in .gbrjob file, so they are not fully free.
 // Use only what is allowed in .gbrjob files.
-// for other colors (user defined), the defined value is the html color syntax.
+// for other colors (user defined), the defined value is the html color syntax
+// and R<integer>G<integer>B<integer> In gbrjob file.
 static FAB_LAYER_COLOR solderMaskColors[]  =
 {
     { _HKI( NOT_SPECIFIED ), wxColor( 80, 80, 80 ) },   // Not specified, not in .gbrjob file
@@ -71,7 +72,6 @@ static FAB_LAYER_COLOR solderMaskColors[]  =
     { _HKI( "Black" ), wxColor( 20, 20, 20 ) },         // used in .gbrjob file
     { _HKI( "White" ), wxColor( 200, 200, 200 ) },      // used in .gbrjob file
     { _HKI( "Yellow" ), wxColor( 128, 128, 0 ) },       // used in .gbrjob file
-    { _HKI( "Purple" ), wxColor( 100, 0, 100 ) },       // used in .gbrjob file
     { _HKI( USER_DEFINED ), wxColor( 128, 128, 128 ) }, //free. the name is a dummy name here
     { "", wxColor( 0, 0, 0 ) }                          // Sentinel
 };
diff --git a/pcbnew/exporters/gerber_jobfile_writer.cpp b/pcbnew/exporters/gerber_jobfile_writer.cpp
index 566094c2ff..448dca46e8 100644
--- a/pcbnew/exporters/gerber_jobfile_writer.cpp
+++ b/pcbnew/exporters/gerber_jobfile_writer.cpp
@@ -657,7 +657,18 @@ void GERBER_JOBFILE_WRITER::addJSONMaterialStackup()
         if( item->IsColorEditable() && uptodate )
         {
             if( !item->m_Color.IsEmpty() && item->m_Color != NOT_SPECIFIED )
-                addJSONObject( wxString::Format( "\"Color\":  \"%s\",\n", item->m_Color ) );
+            {
+                wxString colorName = item->m_Color;
+
+                if( colorName.StartsWith( "#" ) )     // This is a user defined color.
+                {
+                    // In job file a color can be given by its RGB values (0...255)
+                    wxColor color( colorName );
+                    colorName.Printf( "R%dG%dB%d", color.Red(), color.Green(), color.Blue() );
+                }
+
+                addJSONObject( wxString::Format( "\"Color\":  \"%s\",\n", colorName ) );
+            }
         }
 
         if( item->IsThicknessEditable() && uptodate )
@@ -672,8 +683,8 @@ void GERBER_JOBFILE_WRITER::addJSONMaterialStackup()
             // Do not add constrains that create more expensive boards.
             if( brd_stackup.m_HasDielectricConstrains )
             {
-                addJSONObject( wxString::Format( "\"DielectricConstant\":  %.1f,\n", item->m_EpsilonR ) );
-                addJSONObject( wxString::Format( "\"LossTangent\":  %f,\n", item->m_LossTangent ) );
+                addJSONObject( wxString::Format( "\"DielectricConstant\":  %s,\n", item->FormatEpsilonR() ) );
+                addJSONObject( wxString::Format( "\"LossTangent\":  %s,\n", item->FormatLossTangent() ) );
             }
 
             PCB_LAYER_ID next_copper_layer = (PCB_LAYER_ID) (last_copper_layer+1);