in a crt monitor the tube projects a stream of electrons. Since you are in physics you should know that different colors have different wave lengths. it projects electrons in certain wavelengths and than it can appear on the screen because it is coated with a phosphorus type substance which acts as a medium for it to be displayed.
Ill give a verrrrrrry quick description for you... just google key words
chromanace and lumanance((electronic info) are sent in and streamed out the cathode ray tube and a series of other parts (ie. anode) then it starts scaning the ray on whats called a raster which is coated with phosphorus (red green blue) and the pixles are "excited". It then does scanning which consistes of vertical and horizontal blanking. There are two types of scanning methodes interlaced and progressive.