> 3. Colours is the single most important thing of design
Colors are indeed the important aspect of design, but they're also hard to choose and understand. In general, you have to know some things about colour theory when choosing a palette. I'd recommend to you to choose a popular palette from the sites I referred to in the article. Another option is to find a nice presentation and copy its palette. Speaker Deck is definitely your go-to choice for this.
>Just a tip here: not all palettes work well for a presentation. Firstly, some palettes have too much contrast.
Contrast is (simply put) the difference between two colors. It is often used to create vivid and colorful images, example: http://www.flickr.com/photos/louisgely/4409863711/in/photost.... That might work great for art and photography, but it's not easy for our eyes. In fact, when you're having a too contrasty palette it might look great on your computer but it will be difficult for viewers to read it comfortably. Also, consider that the projectors usually have different color profiles and not having enough contrast could become an even bigger problem. Generally you need a nice balanced palette eg. https://speakerdeck.com/geeforr/whats-new-in-ruby-2-dot-0. Finally, when you're using only black and white in your palette, everything looks plain and emotionless, at least to me.
To conclude, colors are hard but there are ways to find good palettes around.
P.S.: I should edit my original post and clarify these things, add some examples as well.