For flags with all three colours:
SELECT flagName
FROM Flags
WHERE
flagID IN
(
SELECT Juntion.fkFlags
FROM Juntion INNER JOIN Colours ON Juntion.fkColours = Colours.colourID
WHERE Colours.colour = "Red"
)
AND flagID IN
(
SELECT Juntion.fkFlags
FROM Juntion INNER JOIN Colours ON Juntion.fkColours = Colours.colourID
WHERE Colours.colour = "White"
)
AND flagID IN
(
SELECT Juntion.fkFlags
FROM Juntion INNER JOIN Colours ON Juntion.fkColours = Colours.colourID
WHERE Colours.colour = "Blue"
)
Similarly, for common colours between two flags
SELECT colour
FROM Colours
WHERE
colourID IN
(
SELECT Juntion.fkColours
FROM Juntion INNER JOIN Flags ON Juntion.fkFlags = Flags.flagID
WHERE Flags.flagName = "Stars and Stripes"
)
AND colourID IN
(
SELECT Juntion.fkColours
FROM Juntion INNER JOIN Flags ON Juntion.fkFlags = Flags.flagID
WHERE Flags.flagName = "Jolly Roger"
)