"We have a black and white dog."
Translation:Nous avons un chien noir et blanc.
The Duo machine doesn't like rearranging word order for two reasons. One, it would take an exponential amount of increased programming to make it possible. Second, Duo has no way of knowing if you are reading the words correctly or really understand them.
You may be satisfied that you know black and white in French and English but the only way Duo can know this for sure is if you type it in the order it was given to you.
Two extraordinarily famous French composers (Debussy and Satie) separately wrote pieces of music under the title Blanc et Noir. Take out all references to the work of Debussy and/or Satie and the number of google results for blanc et noir is considerably reduced. Take out similar brand names and then you will find most of the entries under blanc et noir turn out to be noir et blanc.
I'm not in a high level of french (or even english) and I'm not sure; but I think, though your sentence MEANS the SAME thing, but its EXACT translation would be : "we have a dog, IT IS black and white". u see that IT IS is excessive. in the original sentence "black and white" is the adj of "chin" but in yours, "it is black and white" is a distinct sentence. u might meant to say: "we have a dog THAT is ...". I'm not sure but I think ur sentence is correct as an informal one but a more correct french might be: "nous avons un chin QU'IL EST ...".
As far as I understand, "Nous avons" and "On a" are interchangeable. However, notice that the verbs are in correct conjucation... So it is not "instead of nous" per se.
Duolingo (acts weird and) assumes that you pick the conjugation correctly and messed up the pronoun; however, most of the time you pick the pronoun correctly and mess up the conjugation.
So, long story short, it would be more appropriate, if they correct "Nous a" into "Nous avons" instead of "On a". This is confusing for beginners (like myself).