cold solder joint is where the solder starts cracking and doesn't make good contact or in some cases no contact at all. you can often times sniff this out by tapping on your cab and see if the picture will shake or primary colors appear/disappear. depending on the effect you see from the tapping will usually steer you in the direction of what to look for. a missing color for instance will either be in the neckboard color drive circuitry (the drive transistors, resistors) or in the video signal header itself (the R G B pins).
if you get no red until the monitor warms up then it's more than likely, as I said before, a problem with your tube. the red gun either being weak or dirty. only a monitor rejuvenator can tell.