Update default matcap (#23126)

src/renderers/shaders/ShaderLib/meshmatcap.glsl.js

@@ -90,7 +90,7 @@ void main() {
 
 	#else
 
-		vec4 matcapColor = vec4( 1.0 );
+		vec4 matcapColor = vec4( vec3( mix( 0.2, 0.8, uv.y ) ), 1.0 ); // default if matcap is missing
 
 	#endif