The white waist coat surely has two versions. One is the casual look options and the other one for a formal style statement. Let us discuss both your options!
1) Formal look
If you wish to impress someone or come out of your shell and prove yourself to be a responsible and mature adult or you wish to go a responsible and mature way when it come to fashion, this is perfect for you. Wear a smart shirt with a tie and add in your white waistcoat. This will give you the smart suited appearance without the suit. On days its just too hot for a suit jacket, this is your best bet. White adds elegance and class.
2) Casual look
When it comes to waistcoats the decision is tricky. If you opt for a color then there are restrictions on the shirts it will be compatible with or even t-shirts. If you opt for black then you may just run into a server with a similar waist coat so you can take a different route by opting for white. This look is smart and as smart as casual clothing can get. You get the smart date look or party style without the added bomber jacket or suit jacket options. This is basically a formal look but minus the commitment!