This page will help you to adjust your screen for colour and position.
It is not necessary for this circle to be in the centre of the screen. Hold a CD or something else that is circular against it.

Trying to define what is Blue or Red, or Green is a matter of opinion and one man's green will be another man's blue. The best that can be done is maka a comparison between each colour and compare them to a "known" value: that is a Microsoft screen colour.
The colours shown below are as follows:
The blue should match the colour of the Toolbar at the bottom of your screen.
The grey should match the bar above it.
The orange is the colour of the small "Close Window" X.
The green is the colour of the Start button