Hi,
the armor dyes work as follows:
- there's a starter set that is available from the time you create your character, they are basic colors around the spectrum
- as you adventure in the world you can occasionally get an unidentified dye drop. if you open it, it will generate a random color dye. At that point you can either use that dye to make it permanent for your character or sell it on trading post. (the drop rate is available from anything you kill or loot, and the find rate is around 5% I think, but it's my guess)
- as mentioned above, once the dye has been identified, it can be sold, so you can actually shop for specific colors on the trading post. Many dyes cost very little amount of money, so you can expand the starter set dye set very quickly for little money. Only rare and popular dyes cost a lot, such as pure black and pure white colors (but the prices have been coming down).
So, to answer whether the dyes are rare, there are different classes of dyes, common, uncommon, and rare. So, obviously rare ones will be rare, but with that said they are available to be bought on the Trading Post if you have the gold for it. So, from a players point of view, dyes aren't really rare, some colors are valued highly by the community and thus take a while to obtain (because you need to save up money to buy them).
As far as which class is easiest, I'd say any class is rather straight forward and easy to figure out except mesmer. If this your first MMO, don't pick mesmer on the first try.
I would say pick warrior, guardian or ranger class. Those are the most straight forward classes. If you like scholastic mage classes, I believe elementalist is the easiest of the three (elementalist, necromancer and mesmer are the three scholar classes in the game). Engineer and thief as relatively easy as well, except their mechanics might be a bit cumbersome to figure out for a novice, but they are by no means hard.
I hope that answers your questions. If you'd like more info let me know.