use colouring defaults from graphite-web-1.10

--- carbonapi-0.3.0/expr/functions/cairo/png/picture_params.go
+++ carbonapi-0.3.0/expr/functions/cairo/png/picture_params.go
@@ -351,10 +351,10 @@
 	Height:     250,
 	Margin:     10,
 	LogBase:    0,
-	FgColor:    "white",
-	BgColor:    "black",
-	MajorLine:  "rose",
-	MinorLine:  "grey",
+	FgColor:    "black",
+	BgColor:    "white",
+	MajorLine:  "grey",
+	MinorLine:  "rose",
 	FontName:   "Sans",
 	FontSize:   10,
 	FontBold:   FontWeightNormal,
@@ -414,8 +414,8 @@
 	LeftDashed:  false,
 	LeftColor:   "",
 
-	MajorGridLineColor: "white",
-	MinorGridLineColor: "grey",
+	MajorGridLineColor: "grey",
+	MinorGridLineColor: "rose",
 }
 
 var templates = map[string]PictureParams{
@@ -424,10 +424,10 @@
 		Height:     250,
 		Margin:     10,
 		LogBase:    0,
-		FgColor:    "white",
-		BgColor:    "black",
-		MajorLine:  "rose",
-		MinorLine:  "grey",
+		FgColor:    "black",
+		BgColor:    "white",
+		MajorLine:  "grey",
+		MinorLine:  "rose",
 		FontName:   "Sans",
 		FontSize:   10,
 		FontBold:   FontWeightNormal,
@@ -487,7 +487,7 @@
 		LeftDashed:  false,
 		LeftColor:   "",
 
-		MajorGridLineColor: "white",
-		MinorGridLineColor: "grey",
+		MajorGridLineColor: "grey",
+		MinorGridLineColor: "rose",
 	},
 }