I18N: Improve the context for color-related strings in WP_Theme::translate_header().

* Use the `color scheme` context for the "Light" string, for more accuracy.
* Add the same context to the "Dark" string too, for consistency.

Follow-up to [37946], [52588].

Fixes #54804.

git-svn-id: https://develop.svn.wordpress.org/trunk@52603 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-theme.php

@@ -981,8 +981,8 @@ final class WP_Theme implements ArrayAccess {
 						'tan'               => __( 'Tan' ),
 						'white'             => __( 'White' ),
 						'yellow'            => __( 'Yellow' ),
-						'dark'              => __( 'Dark' ),
-						'light'             => _x( 'Light', 'color' ),
+						'dark'              => _x( 'Dark', 'color scheme' ),
+						'light'             => _x( 'Light', 'color scheme' ),
 						'fixed-layout'      => __( 'Fixed Layout' ),
 						'fluid-layout'      => __( 'Fluid Layout' ),
 						'responsive-layout' => __( 'Responsive Layout' ),