by default modebar colors contrasts with paper_bgcolor

Author: antoinerg

src/plots/layout_attributes.js

@@ -237,21 +237,18 @@ module.exports = {
         bgcolor: {
             valType: 'color',
             role: 'style',
-            dflt: 'rgba(255, 255, 255, 0.7)',
             editType: 'modebar',
             description: 'Sets the background color of the modebar.'
         },
         color: {
             valType: 'color',
             role: 'style',
-            dflt: 'rgba(0, 31, 95, 0.3)',
             editType: 'modebar',
             description: 'Sets the color of the icons in the modebar.'
         },
         activecolor: {
             valType: 'color',
             role: 'style',
-            dflt: 'rgba(0, 22, 72, 0.5)',
             editType: 'modebar',
             description: 'Sets the color of the active or hovered on icons in the modebar.'
         },

src/plots/plots.js

@@ -1335,9 +1335,9 @@ plots.supplyLayoutGlobalDefaults = function(layoutIn, layoutOut, formatObj) {
     coerce('datarevision');
 
     coerce('modebar.orientation');
-    coerce('modebar.bgcolor');
-    coerce('modebar.color');
-    coerce('modebar.activecolor');
+    coerce('modebar.bgcolor', Color.addOpacity(layoutOut.paper_bgcolor, 0.5));
+    coerce('modebar.color', Color.contrast(layoutOut.modebar.bgcolor, 30, 30));
+    coerce('modebar.activecolor', Color.contrast(layoutOut.modebar.bgcolor));
 
     Registry.getComponentMethod(
         'calendars',