(SP)Lighting.vert: clarify comment regarding material colors

jme3-core/src/main/resources/Common/MatDefs/Light/Lighting.vert

@@ -126,7 +126,8 @@ void main(){
       DiffuseSum  =  m_Diffuse  * vec4(lightColor.rgb, 1.0);
       SpecularSum = (m_Specular * lightColor).rgb;
     #else
-      AmbientSum  = g_AmbientLightColor.rgb; // Default: ambient color is dark gray
+      // Defaults: Ambient and diffuse are white, specular is black.
+      AmbientSum  = g_AmbientLightColor.rgb;
       DiffuseSum  =  vec4(lightColor.rgb, 1.0);
       SpecularSum = vec3(0.0);
     #endif

jme3-core/src/main/resources/Common/MatDefs/Light/SPLighting.vert

@@ -117,6 +117,7 @@ void main(){
         SpecularSum = m_Specular.rgb;
         DiffuseSum = m_Diffuse;                   
     #else
+        // Defaults: Ambient and diffuse are white, specular is black.
         AmbientSum  = g_AmbientLightColor.rgb; 
         SpecularSum = vec3(0.0);
         DiffuseSum = vec4(1.0);