Write SQL query to solve given problem: On image no. 99 identify the percentage of objects that are described as white.. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT CAST(SUM(CASE WHEN T2.ATT_CLASS = 'white' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(OBJ_SAMPLE_ID) FROM IMG_OBJ_ATT AS T1 INNER JOIN ATT_CLASSES AS T2 ON T1.ATT_CLASS_ID = T2.ATT_CLASS_ID WHERE T1.IMG_ID = 99