I think most commenters seem to think Duo is being unnecessarily restrictive here.
The way he pronounces "rouge" on the slowed down track is a bit bizarre. It sounds completely different from the normal speed track. Like he adds an entire syllable, like a garbled "un" in there. ANyone else hear this?
in English , "that is red" = "that is the color red" since RED is RED so both should surely be marked as correct
"That color is red" seems like it should be a perfectly acceptable translation. Why is it not?
Is this an accurate way of saying this in French? As many have pointed out, it is a bit awkward translated back in English. I guess "C'est rouge" isn't really acceptable?