I guess if the context were about a specific violet, like the third one from the left in a bunch of them, then you would il. The question, as I understand it, is asking about violets in general. Sometimes in French you use the singular in this case, where in English you would use plural.

Hi Chris.

Thanks for your reply. I thought violet in this context meant "purple". Or does it, in fact, refer to the flower ?

You are probably right. Could refer to the color, too. In that case it is the same kind of reasoning. The general color asks for ce instead of il.