Some of the presentations have been really goo, others really quite bad, visually speaking. The important thing that needs be done prior to uploading it to the presentation computer is to ensure that your presentation is likely to be visually engaging, given the emvironment of the venue. This means that one should take not of the visual problems of previous presentations and take appropriate action (changing font, colors, etc.). Then, when you have a chance to run through the presentation on the presentation computer, tweak things as necessary.
Although a plain black-test-on-a-white-background is quite boring, it is the one that is the most simple to read with simplicity. Darker backgrounds means that one's font needs to be even more contrasting, and possibly either larger or wider.