this should have been covered in your class before this, I will tell you how are candidates have been instructed (I think I just answered the same question twice this week, did you do a search?). It depends on if baptism is by immersion or by pouring.
Our candidates arrive dressed in gym shorts and t-shirt or tank-top (ladies please were proper foundation garment, and don’t wear white, we are not doing a wet t-shirt contest), and flip flops. Over this they wear a grey cotton “poncho” which we have given them, which represents the penitential garb of lent. At the time of baptism the sponsor helps remove this robe, helps you step into the tub, where you kneel, cross your arms and bend over. It is not full immersion because this is a temporary tub, but Father uses a LOT of water, you will be soaked. then the sponsor helps you out, wraps you in a towel, you walk to the back of the church out to the dressing area. There you have already stored your first communion/confirmation outfit. For ladies we suggest a dress or suit, the typical “Easter” outfit is fine. We supply the white garment for the baptism symbol, so you can wear any color. Girls usually wear a typical first communion dress.
Men and boys we ask for white shirt, dress pants and shoes, suit is great but not mandatory.
Girls are well advised to wear hair simply, not to spend money on a do because it will get wet, don’t wear mascara or make-up either. French braid is good for long hair, or use clips. Remember bangs should be off the forehead for the confirmation anointing too,
We like you to dress as quickly as possible after Baptism, so consider simplicity and ease of dressing when you select your outfit. dont forget dry underwear, shoes and stockings, and a comb if you need it.
why not call the parish office today and find out how the baptism is to be done? if just by pouring on the forehead, still keep hairdo simple, but a dress or suit, or blouse and skirt is fine. Modesty is the key element here, not color, although white blouse would be traditional.