Colour can add a visual punch to your poster. Aim for good contrast between text and background colours to ensure readability. That said, beware that some contrasting colour combinations are easier to read than others.
Overuse of colours and a lack of contrast between text and background work against readability in the first poster below. Arranging the text into columns would also help greatly to organize the content.
This example uses a single colour (red) as an element to define the columns. The text has good contrast with the background and is easy to read.