So one thing I love about flashes is putting colour gels on them to give them funky looks. Gels are essentially bit of colour cellophane which you attach to your flash to change its colour. They can be great for adding some cool effects to your shots. The following are a few shots I took using two separate flashes, each with a different colour gel. This way I mostly get two separate colours going on in my photographs.
Your settings can vary depending on the situation. If you have a room that's fairly well lit, you can mimic darkness by choosing a higher shutter speed to cut out the ambient light, similar in the way we would mix flash with ambient light outside during the day. I generally shoot anything with flash on full manual so adjust your shutter depending on the level of ambient light you want to see. To test it out, take a couple of shots using your settings but without the flashes, if you get a black image this means there will be no ambient light coming into your final shot. The flashes shouldn't been too affected by the faster shutter as they're mostly controlled by your aperture. ISO 100 should be fine, you can change it depending on the circumstances, but generally stick to 100 for this sort of thing.
In some instance, colours don't always work so do use your judgement to see whether they're giving the look you want or not. You don't have to have both your flashes in colours, you can choose to just use one flash with a colour gel instead and this way you can add tinges of colour to your subject. Sometimes I like to set up the coloured flash behind the subject and a white flash in front of them to give them a colour outline, or you could skip the front light and just go for a coloured outline. Examples below:
So if you like what you see, grab yourself a pack of flash gels and try it out for yourself. Gels can be pretty cheap and can give you a lot of flexibility in what you can do. So go out there and create something for yourself.