Translation:Red, yellow, and orange are fall colors.
You're right: the words "žlutá a" pretty much blend together in the audio at normal speed. However, the words are clearly separated in the slow audio (when given for dictation).
I wrote: ...are colours of the autumn. It was marked wrong. Is it better to say "autumn colours"?
this is genetive there is no reason not to also accept colors of autumn, or colors of fall.