Question: On image no. 99 identify the percentage of objects that are described as white.
SQL: 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