Read up exactly what the judge is looking for in these types of classes, go to a couple shows and watch. Make a note based upon the criteria of whatever governing body you have, says what kind of horses should place and make your own judgement. Stick around, listen to how the judge places the horses. If your list and the judges list don't match up, approach the judge after the show, tell them you weren't riding but interested in learning why they placed the horses the way they did.
Most judges are really nice, and super knowledgeable and are more then happy to impart their know-how on others.
You'll find that 99% of the judges actually know what they are looking for, they are color blind so to speak when it comes to judging, meaning that they see color as not part of the reason why they chose a horse (as in its all about quality of gait, suitability, obediance, cleanliness, before its ever about.. whose pony has the best color).
You'll always find judges you don't agree with and don't show under them, then you'll have nothing to complain about.
Gordon Wright once told a student to take up swimming because he would never be a good rider, that rider was George Morris.