fix mergeGeometries

Author: dongho-shin

src/core/utils/mergeGeometries.js

@@ -205,7 +205,20 @@ export function mergeGeometries( geometries, options = {}, targetGeometry = new
 			const attr = geometry.getAttribute( key );
  			if ( ! skip ) {
 
-				copyAttributeContents( attr, targetAttribute, offset );
+				if ( key === 'color' && targetAttribute.itemSize !== attr.itemSize ) {
+
+					//make sure the color attribute is aligned with itemSize 3 to 4
+					for ( let index = offset; index < attr.count; ++ index ) {
+
+						attr.setXYZW( index, targetAttribute.getX( index ), targetAttribute.getY( index ), targetAttribute.getZ( index ), 1.0 );
+
+					}
+
+				} else {
+
+					copyAttributeContents( attr, targetAttribute, offset );
+
+				}
 
 			}