It's because you're calling the input function from the if statement. Call input one time, store it in a variable, then compare that. Something like:
color = input()
if color == 'bright green':
elif color == 'red'
Basically what you're doing in the provided example is asking the user for input in the "if" line, comparing that to 'bright green' then asking for a separate input and comparing that to 'red'. As an example, try typing "red" then "bright green". You should get no output at all