Doesn't matter how old you are, first date (of a new possible relations) is always exciting and important. It will show whether second date will happen. In this case first impression you make will mean a lot.
So what to wear for the first date to make right impression?
Depending of your age and status, recommendations will be different. Let's assume the most difficult situation, when you have your first date in the end of day after work. In this case you will be quite limited with choices as have to look appropriate for both office work at the day time and for romantic personal event.
The most promising situation. Say, you have just met an interesting guy in the university and going for the first date after study hours to the university cafe for a drink together. These all happened so fast and totally unexpected, you have no time to drop by home and dress up purposely.
The only advice for this situation, just be ready at any day. Spend a few minutes at home before university to plan your outfit and hair style to look nice and neat. If suddenly you meet your future husband, you will be sure you look your best.
Working lady, probably having senior position in the company
As a senior, you are quite restricted by your position in the choices of outfits even if there is no dress code in your company.
So your outfit for the first date has to be acceptable for the office. However, you still may afford some outfit variations on senior position.
Soft grey color will be a good option. It looks enough formal to wear in the office while it's not too formal for the personal event. It makes good color combination with soft pink. If you pair it with white, your outfit might be too office looking what has to be avoided at the first date. Also light pink will create a soft romantic mood, and its exactly your purpose, isn't it? Another advantage of side punk color is it makes refreshing effect when worn near the face. After a long working day it might be just nice.
Young working lady
You might be even more restricted with office dress code and cannot allow much of variations. In this case, the only you can do is to liven up formal office with statement accessories (scarves, belts, bags, necklaces etc.). Keep them in the bag during office hours and put on for the first date. They will make you look special and unforgettable.