Você pode usar dbms_lob.instr para esta finalidade, ou seja,
select * from table_name
where dbms_lob.instr(blob_field, utl_raw.CAST_TO_RAW('00ff00ff'), 1, 1) > 0
select * from table_name
where dbms_lob.instr(blob_field, utl_raw.CAST_TO_RAW('00ff00ff'), 1, 1) > 0
