src/main/java/org/embulk/parser/poi_excel/visitor/AbstractPoiExcelCellAttributeVisitor.java in embulk-parser-poi_excel-0.1.3 vs src/main/java/org/embulk/parser/poi_excel/visitor/AbstractPoiExcelCellAttributeVisitor.java in embulk-parser-poi_excel-0.1.4

@@ -122,9 +122,12 @@
 		}
 		Object value = supplier.get(column, cell, source);
 
 		if (value instanceof Color) {
 			int rgb = PoiExcelColorVisitor.getRGB((Color) value);
+			if (rgb < 0) {
+				return null;
+			}
 			if (column.getType() instanceof StringType) {
 				value = String.format("%06x", rgb);
 			} else {
 				value = (long) rgb;
 			}