When using OpenGL, you can set the colour by using glColor3f(real,real,real);
What this does is to set the colour in the RGB form with the first parameter for the amount of Red, the second for Green and the third for Blue. Those three values must be anywhere between 0.0 and 1.0. That should give you all the colours!

hope it helps

PS: btw tht is part of the tutorial!