It just does not look right

There is a component to visual design that cannot be learnt from studying books. On some presentations/slides I can spend a lot of time, because they simply do not look right, even if the content is pretty simple. And the worst thing, I cannot tell why.

After fiddling with a number of parameters, things can all of a sudden start to look acceptable:

• Changing the balance in the colour scheme, often focusing on grey with just one strong accent colour, instead of using all the colours that are available in the corporate colour scheme.
• Using lighter colour/shades in slide shapes
• Making all images black and white
• Endless repositioning of slide shapes to get the balance right
• Reducing the font size (yes, you read it right), and/or rebalancing the number of words in one line

Why? I do not know, it somehow works...