Colours

What looks good on the screen may not work so well when it is projected.  Even today, most projectors lose some of their colour density when they are projected.  This makes the screen look washed out.  Pale colours are very susceptible to this effect.

The most readable colours are yellow writing on a dark blue background or black writing on a yellow background.  If you use a plain background, the text will be more readable but the slides look less interesting.

Be careful with using images as a background, it is very difficult to choose a text colour that will always show up.  If you want to use images as backgrounds, to reflect for instance the different industries your customers are in, I suggest making them very pale, more like a watermark so that the black text will show up against the whole background.

In PowerPoint or similar software, it can help to use a shadow font, which will provide more contrast between the text and the background.