You are now a sqlite data analyst, and you are given a database schema as follows:

    【Schema】
    【DB_ID】 superhero
【Schema】
# Table: hero_power
[
(hero_id:INTEGER, Examples: [1, 2, 3]),
(power_id:INTEGER, Examples: [1, 18, 26])
]
# Table: colour
[
(id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(colour:TEXT, Examples: [No Colour, Amber, Auburn])
]
# Table: superpower
[
(id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(power_name:TEXT, Examples: [Agility, Accelerated Healing, Lantern Power Ring])
]
# Table: publisher
[
(id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(publisher_name:TEXT, Examples: [ABC Studios, Dark Horse Comics, DC Comics])
]
# Table: superhero
[
(id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(superhero_name:TEXT, Examples: [3-D Man, A-Bomb, Abe Sapien]),
(full_name:TEXT, Examples: [Charles Chandler]),
(gender_id:INTEGER, Examples: [1, 2, 3]),
(eye_colour_id:INTEGER, Examples: [9, 33, 7]),
(hair_colour_id:INTEGER, Examples: [13, 1, 4]),
(skin_colour_id:INTEGER, Examples: [1, 7, 23]),
(race_id:INTEGER, Examples: [1, 24, 33]),
(publisher_id:INTEGER, Examples: [13, 3, 4]),
(alignment_id:INTEGER, Examples: [1, 2, 3]),
(height_cm:INTEGER, Examples: [188, 203, 191]),
(weight_kg:INTEGER, Examples: [90, 441, 65])
]
# Table: attribute
[
(id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(attribute_name:TEXT, Examples: [Intelligence, Strength, Speed])
]
# Table: hero_attribute
[
(hero_id:INTEGER, Examples: [1, 2, 3]),
(attribute_id:INTEGER, Examples: [1, 2, 3]),
(attribute_value:INTEGER, Examples: [80, 75, 95])
]
# Table: alignment
[
(id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(alignment:TEXT, Examples: [Good, Bad, Neutral])
]
# Table: race
[
(id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(race:TEXT, Examples: [-, Alien, Alpha])
]
# Table: gender
[
(id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(gender:TEXT, Examples: [Male, Female, N/A])
]
【Foreign keys】
hero_power.hero_id=superhero.id
hero_power.power_id=superpower.id
superhero.alignment_id=alignment.id
superhero.eye_colour_id=colour.id
superhero.gender_id=gender.id
superhero.hair_colour_id=colour.id
superhero.publisher_id=publisher.id
superhero.race_id=race.id
superhero.skin_colour_id=colour.id
hero_attribute.attribute_id=attribute.id
hero_attribute.hero_id=superhero.id

    【Question】
    In superheroes with missing weight data, calculate the difference between the number of superheroes with blue eyes and no eye color. missing weight data refers to weight_kg = 0 OR T1.weight_kg = NULL; difference = SUBTRACT(SUM(colour.id = 7), SUM(colour.id = 1)); blue eyes refers to eye_colour_id WHERE colour.id = 7; no eye color refers to eye_colour_id WHERE colour.id = 1;

    【Evidence】
    missing weight data refers to weight_kg = 0 OR T1.weight_kg = NULL; difference = SUBTRACT(SUM(colour.id = 7), SUM(colour.id = 1)); blue eyes refers to eye_colour_id WHERE colour.id = 7; no eye color refers to eye_colour_id WHERE colour.id = 1;

    Please read and understand the database schema carefully, and generate an executable SQL based on the user's question and evidence. 

SQL: SELECT SUM(CASE WHEN T2.id = 7 THEN 1 ELSE 0 END) - SUM(CASE WHEN T2.id = 1 THEN 1 ELSE 0 END) FROM superhero AS T1 INNER JOIN colour AS T2 ON T1.eye_colour_id = T2.id WHERE T1.weight_kg = 0 OR T1.weight_kg is NULL