agreement of adjectives when two adjectives describe the same noun

Question

Bonjour!
I thought that if two adjectives were being used to describe the same noun, then you wrote these adjectives both in the masculine form, even if the noun is feminine, e.g. Elle a acheté une nouvelle robe blanc et noir.
Yet, the correct answer in a quizz I did was "les canines blanches et pointres", not "blancs et pointres".
Can someone please explain this?
Cheryl.

Accepted Answer

Hi Cheryl
Just to add to what Ron said - your first example would be,  une robe blanche et noire.
I think the rule you are thinking off is when  you use a modified colour like light /dark/royal/navy blue...
Then there is no agreement. i.e. 
Des yeux bleu clair
Une robe bleu marine
Hope this helps!

Answer

Bonjour Cheryl,
I am unaware of a grammar rule that specifies two adjectives used to describe the same noun being in  masculine form, even if the noun is feminine.  In the example given, «les canines» refers to the canine teeth which are feminine and hence the adjectives would agree in the feminine endings.
Bonne chance,