Re: Wearing black on engagement?
I have been told quite several times that black is associated with mourning and that one shouldn’t wear it on happy occasions but I totally disagree this! Also you may have seen that there are women (specially at the side of India) start wearing white color when their husband pass away or things like that.
I understand we may be careful while attending funerals too by not wearing too bright or shocking colors but if one appears in pink or red doesn’t mean she has no grief for her relative!!
Black is a really beautiful and elegant color and also Kaaba Sharif has a Black beautiful cover! why not think about that? White is a very beautiful and pure color and it is the favorite color of Our Holy Prophet PBUH. 
Wear every color.. according to the occasion but please do not associate it with mourning or happiness. Its your heart where you feel grief or happiness but not the color of your dress!