Mysql Function returning same value

I am in need of mysql function but gives same value every time
this mysql function gives me same value every time i.e. S_Start_ToBeStarted (Value of 1st If)

-- colorA
DELIMITER $$
DROP FUNCTION IF EXISTS `colorA`$$
CREATE FUNCTION `colorA`( 
    Appf VARCHAR(3), 
    Start_Datef DATETIME, 
    PDCf DATETIME
    ) RETURNS INT
    DETERMINISTIC
BEGIN
DECLARE finalcolor INT DEFAULT 0;
IF Appf = 'Yes' & IFNULL(Start_Datef, 'NULL' = 'NULL' & sysdate() <= PDCf
    THEN SET finalcolor = (SELECT `PP_Colors`.`S_Start_ToBeStarted` FROM `SCR_Sap`.`PP_Colors` LIMIT 1);

ELSE IF Appf = 'Yes' & IFNULL(Start_Datef, 'NULL') = 'NULL' & sysdate() > PDCf
    THEN SET finalcolor = (SELECT `PP_Colors`.`S_Start_Error` FROM `SCR_Sap`.`PP_Colors` LIMIT 1);

ELSE IF Appf = 'Yes' & IFNULL(Start_Datef, 'NULL') != 'NULL' & sysdate() <= PDCf
    THEN SET finalcolor = (SELECT `PP_Colors`.`S_Start_Ok` FROM `SCR_Sap`.`PP_Colors` LIMIT 1);

ELSE IF Appf = 'Yes' & IFNULL(Start_Datef, 'NULL') != 'NULL' & sysdate() > PDCf
    THEN SET finalcolor = (SELECT `PP_Colors`.`S_Start_LateStarted` FROM `SCR_Sap`.`PP_Colors` LIMIT 1);

ELSE SET finalcolor = (SELECT `PP_Colors`.`S_NotApplicable` FROM `SCR_Sap`.`PP_Colors` LIMIT 1);

END IF;
END IF;
END IF;
END IF;
    RETURN finalcolor;
    END$$
DELIMITER ;