Accent color:

- Demo: added accent color switching to toolbar
- added `FlatLaf.setGlobalExtraDefaults()` for easy setting accent color at runtime

(issue #233)

flatlaf-core/src/main/java/com/formdev/flatlaf/FlatLaf.java

@@ -86,6 +86,7 @@ public abstract class FlatLaf
 	private static final String DESKTOPFONTHINTS = "awt.font.desktophints";
 
 	private static List<Object> customDefaultsSources;
+	private static Map<String, String> globalExtraDefaults;
 	private Map<String, String> extraDefaults;
 
 	private String desktopPropertyName;
@@ -465,11 +466,14 @@ public abstract class FlatLaf
 	}
 
 	protected Properties getAdditionalDefaults() {
-		if( extraDefaults == null )
+		if( globalExtraDefaults == null && extraDefaults == null )
 			return null;
 
 		Properties properties = new Properties();
-		properties.putAll( extraDefaults );
+		if( globalExtraDefaults != null )
+			properties.putAll( globalExtraDefaults );
+		if( extraDefaults != null )
+			properties.putAll( extraDefaults );
 		return properties;
 	}
 
@@ -785,6 +789,38 @@ public abstract class FlatLaf
 		customDefaultsSources.remove( folder );
 	}
 
+	/**
+	 * Gets global extra UI defaults; or {@code null}.
+	 *
+	 * @since 1.6
+	 */
+	public static Map<String, String> getGlobalExtraDefaults() {
+		return globalExtraDefaults;
+	}
+
+	/**
+	 * Sets global extra UI defaults, which are only used when setting up the application look and feel.
+	 * E.g. using {@link UIManager#setLookAndFeel(LookAndFeel)} or {@link #setup(LookAndFeel)}.
+	 * <p>
+	 * The global extra defaults are useful for smaller additional defaults that may change.
+	 * E.g. accent color. Otherwise FlatLaf properties files should be used.
+	 * See {@link #registerCustomDefaultsSource(String)}.
+	 * <p>
+	 * The keys and values are strings in same format as in FlatLaf properties files.
+	 * <p>
+	 * Sample that setups "FlatLaf Light" theme with red accent color:
+	 * <pre>{@code
+	 * FlatLaf.setGlobalExtraDefaults( Collections.singletonMap( "@accentColor", "#f00" ) );
+	 * FlatLightLaf.setup();
+	 * }</pre>
+	 *
+	 * @see #setExtraDefaults(Map)
+	 * @since 1.6
+	 */
+	public static void setGlobalExtraDefaults( Map<String, String> globalExtraDefaults ) {
+		FlatLaf.globalExtraDefaults = globalExtraDefaults;
+	}
+
 	/**
 	 * Gets extra UI defaults; or {@code null}.
 	 *
@@ -811,6 +847,7 @@ public abstract class FlatLaf
 	 * FlatLaf.setup( laf );
 	 * }</pre>
 	 *
+	 * @see #setGlobalExtraDefaults(Map)
 	 * @since 1.6
 	 */
 	public void setExtraDefaults( Map<String, String> extraDefaults ) {

flatlaf-core/src/main/java/com/formdev/flatlaf/util/ColorFunctions.java

@@ -49,6 +49,9 @@ public class ColorFunctions
 
 	/**
 	 * Returns a color that is a mixture of two colors.
+	 * <p>
+	 * This can be used to animate a color change from {@code color1} to {@code color2}
+	 * by invoking this method multiple times with growing {@code weight} (from 0 to 1).
 	 *
 	 * @param color1 first color
 	 * @param color2 second color
@@ -79,6 +82,34 @@ public class ColorFunctions
 			Math.round( a2 + ((a1 - a2) * weight) ) );
 	}
 
+	/**
+	 * Mix color with white, which makes the color brighter.
+	 * This is the same as {@link #mix}{@code (Color.white, color, weight)}.
+	 *
+	 * @param color second color
+	 * @param weight the weight (in range 0-1) to mix the two colors.
+	 *               Larger weight uses more of first color, smaller weight more of second color.
+	 * @return mixture of colors
+	 * @since 1.6
+	 */
+	public static Color tint( Color color, float weight ) {
+		return mix( Color.white, color, weight );
+	}
+
+	/**
+	 * Mix color with black, which makes the color darker.
+	 * This is the same as {@link #mix}{@code (Color.black, color, weight)}.
+	 *
+	 * @param color second color
+	 * @param weight the weight (in range 0-1) to mix the two colors.
+	 *               Larger weight uses more of first color, smaller weight more of second color.
+	 * @return mixture of colors
+	 * @since 1.6
+	 */
+	public static Color shade( Color color, float weight ) {
+		return mix( Color.black, color, weight );
+	}
+
 	/**
 	 * Calculates the luma (perceptual brightness) of the given color.
 	 * <p>

flatlaf-core/src/main/resources/com/formdev/flatlaf/FlatIntelliJLaf.properties

@@ -41,7 +41,7 @@
 Button.focusedBackground = null
 
 Button.default.background = @accentButtonDefaultBackground
-Button.default.foreground = #fff
+Button.default.foreground = contrast($Button.default.background,lighten(@foreground,50%),#fff,50%)
 Button.default.focusedBackground = null
 Button.default.borderColor = shade($Button.default.background,15%)
 Button.default.hoverBorderColor = tint($Button.default.background,50%)