[Python] Dictionary inside/outside for loop

I would like to change one of my elements in the dictionary but if I were to put new_alien outside the loop, all the elements in the dictionary get changed. Why is that?

#ALL aliens get changed when I put put the dictionary up here
new_alien = {'colour': 'green'}

aliens=[]

for alien_number in range(3):
#if i put new_alien here only one alien dictionary gets changed in the for loop (correct code)
#new_alien = {'colour': 'green'}
aliens.append(new_alien)

print(aliens)

for alien in aliens[0:1]:
if (alien['colour'] == 'green'):
alien['colour'] = 'yellow'

print(aliens[0:2])


Output if new_alien is outside the loop:

[{'colour': 'green'}, {'colour': 'green'}, {'colour': 'green'}]
[{'colour': 'yellow'}, {'colour': 'yellow'}]


Output if new_alien is inside the loop:

[{'colour': 'green'}, {'colour': 'green'}, {'colour': 'green'}]
[{'colour': 'yellow'}, {'colour': 'green'}]


Notice how outside the loop all alien dictionary:colour gets changed to yellow.

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