Address feedback: Improve API + add some docs

Author: DmitrySharabin

src/common/color-element.js

@@ -31,6 +31,8 @@ const Self = class ColorElement extends NudeElement {
 	static Color;
 	static all = {};
 	static dependencies = new Set();
+
+	/** @type {Map<string, Color>} */
 	static resolvedColors = new Map();
 
 	static globalStyles = [{ css: baseGlobalStyles }];
@@ -143,6 +145,7 @@ const Self = class ColorElement extends NudeElement {
 	 * Resolve a color value and cache it.
 	 * @param {string} value Color value to resolve.
 	 * @param {Element} element Element to get computed style from to resolve the color value.
+	 * @returns {Color | null} Resolved color value or null if the value cannot be resolved.
 	 */
 	static resolveColor (value, element) {
 		try {
@@ -165,7 +168,7 @@ const Self = class ColorElement extends NudeElement {
 			Self.resolvedColors.set(value, color);
 			element.style.backgroundColor = "";
 
-			return color;
+			return Self.Color.get(color);
 		}
 	}
 };