Add possibility for themes to change text color in header (#12204)

* fixes #12201 add possibility to change text color in header

* fix screenshot

* fix typo in changelog

CHANGELOG.md

@@ -4,6 +4,11 @@ This is the Developer Changelog for Piwik platform developers. All changes in ou
 
 The Product Changelog at **[piwik.org/changelog](https://piwik.org/changelog)** lets you see more details about any Piwik release, such as the list of new guides and FAQs, security fixes, and links to all closed issues. 
 
+## Piwik 3.2.1
+
+### New APIs
+ * Themes can now customize the header text color using `@theme-color-header-text`
+
 ## Piwik 3.2.0
 
 ### New Segments

plugins/CoreHome/stylesheets/layout.less

@@ -47,6 +47,8 @@ nav {
   }
 
   ul a {
+    color: @theme-color-header-text !important;
+
     &:hover {
       text-decoration: none;
     }

plugins/ExampleTheme/stylesheets/theme.less

@@ -3,6 +3,7 @@
 @theme-color-brand: #5793d4;
 @theme-color-background-base: #d9e0e3;
 @theme-color-header-background: #0091ea;
+@theme-color-header-text: #0d0d0d;
 
 @theme-color-widget-title-background: #80d8ff;
 @theme-color-widget-title-text: #01579b;

plugins/Morpheus/stylesheets/theme.less

@@ -16,6 +16,7 @@
 @theme-color-headline-alternative: #4E4E4E;
 
 @theme-color-header-background: #37474f;
+@theme-color-header-text: @color-white;
 
 @theme-color-menu-contrast-text: @theme-color-text;
 @theme-color-menu-contrast-textSelected: @theme-color-menu-contrast-text;