Candid means honest, frank, open, and straightforward in expression. The opposite would be secretive, which means hiding thoughts, feelings, or intentions; not open or frank. 'Miserly' means stingy (related to money). 'Sweet' means pleasant in taste or manner. 'Openly' is actually similar in meaning to candid (an adverb form). 'Private' means personal/secret but is not the direct opposite of the adjective candid.