Grammar fix in use-of-color.html (#3909)

Add missing "the"

understanding/20/use-of-color.html

@@ -30,7 +30,7 @@ <h2>Intent of Use of Color</h2>
          another visual means ensures users who cannot see color can still perceive the information.
       </p>
 
-      <p>Color is an important asset in design of Web content, enhancing its aesthetic appeal,
+      <p>Color is an important asset in the design of Web content, enhancing its aesthetic appeal,
          its usability, and its accessibility. However, some users have difficulty perceiving
          color. People with partial sight often experience limited color vision, and many older
          users do not see color well. In addition, people using limited-color or