It shouldn't as if any place the discoloration on your screen should be on the bottom part of the screen, most crt tvs has a built in deguazer as to when the tv is turn on it is suppose to deguaze the screen, also if you move the tv around at all it can cause this as the earth's magnetic field will do this.
Happens to my moms tv alot as she has it on a swivel base and when she turn the tv a bit around she gets a green patch in the top left corner, next time you see this oval patch show up turn the tv off for about 30 seconds and then turn it back on to see if the color patch is gone.
Also if your tv sits along a wall with a few outlets by it can also cause this but is not as common a problem but i have seen that happen and the person had to move his tv to another area in the living room.
Also if your tv is equipped with the degauze feature it might be starting to get weak in that area of the tube just above as a line runs right around the outer edge of the tube with a small gadget put at eack corner of the tube to degauze the tube, one of those little units may not be working properly anymore, this only applies it your tv is equipped with the degauze feature.
Also make sure no speakers are close to your tv unless they are magnetically sheilded.