It uses very bright contrasting colors.
Try going for a certain color scheme and using different shades of that color and a contrasting color for text.
For example, you could use blue like this forum has, and for headings you can make the table backgrounds darker blue and have the text on the dark blue be white and the text on the light blue be black, or navy. Look at other website color schemes and see what you can come up with.
Also, use colors that aren't quite as "harsh". Some of the blue that I see on your website is, i think, just pure blue (0,0,255), which makes it very bright and not so pleasing to the eyes. Try adding maybe a bit of green and reducing the amount of blue (maybe 0,40,150 or something like that)