Does anyone use one or have a good brand they can recommend? I have never used it before, but I am a bridesmaid in a few weeks time and our dresses are kinda halterneck, so my strap marks are very noticable

I don't want to get a spray tan or do sunbeds so I have been told (by someone in the "know") to use a bit of fake tan on my strap marks and my watch strap mark also. So any tips, pointers or anything? Ideally I'd like to be able to buy a small bottle as this will probably be the only time I'll use it. Also do you get different colours or do you just apply more if you have a darker skin tone?