If you want your audience to be able to see what you have on the slide, there needs to be a lot of contrast between the text colour and the background colour. I suggest a dark background with light text – I usually use a medium to dark blue background and white or yellow letters. Some prefer a light background and dark letters, which will also work well – which you choose will depend on personal preference. Don’t think that just because the text looks fine on your computer screen that it will look fine when projected. Most projectors make colours duller than they appear on a screen, and you should check how your colours look when projected to make sure there is still enough contrast. To check that your colors have enough contrast, use the Color Contrast Calculator.