What smell of olfactory indicator can be detected when we add this in a neutral solution?

An Olfactory indicator is defined as a substance whose smell varies when it is mixed with an acidic or basic solution.Such substances can be used in the laboratory to test whether a solution is a base or an acid, and this process is called olfactory titration. All onion,clove oil and vanilla extract are examples.An olfactory indicator works on the principle that when an acid or base is added to it,then different odour can be detected in bases whereas odour remains same in acids.Certain substances changes odour in acidic or basic medium.

But in acids they retain their characteristic smell!! I am asking if we add olfactory indicator with a neutral solution then what smell will be generated and how do we differentiate whether the given solution is acid or a neutral solution?