"Your coat is light."
Translation:Ton manteau est clair.
Okay, but the statement is that the coat is "light". In English this can refer to being "light" as in light in color or "light" as in light weight or not heavy. The sentence does not specify, so, from the choices provided, it could have been all three of them depending on which way the word was meant. To mark "leger" wrong is totally unfair. This is an unproductive way to help me learn French. I have learned the difference in "leger" and "clair", but, for the exercise, I have only learned what Duolingo wants and to memorise to pass the lesson.
Well, the translation into English from French is "light coat" without any context, but "légèr" is what I would use to mean "light-weight" and "clair" for colour. And so I have to assume it's light in colour, not weight....but if one is translating from English into French, without context, then DL should not mark it wrong. If that happens, however, you can report it and DL is great about adjusting answers for its followers if they are correct. Besides, es ist kostenlos!!!
Surprise! "Leger" does mean light in weight, but "clair" means light in color as well as "clear." Duo will often throw in things you haven't been specifically taught. Often, the only thing you can do is look at the choices and, if one kind of looks possible but it's a usage you've never seen before, guess. You've got a 50/50 chance. I too find it frustrating to get something wrong on an exercise because it hasn't been taught to you, but I suppose the designers of Duo must believe that the pain will help you to learn the new usage more quickly.
Sometimes Duo tries to figure out how you meant to phrase your answer and it suggests the closest correct version it has. "Ta manteau est claire" is wrong because "manteau" is masculine. It should be "ton manteau est claire." But since you used "ta," Duo decided that you meant to use a feminine noun, so it suggested "veste," which means "jacket," not "coat," because it's feminine.