What's the scoop? greens and blues? What are they? I've seen whites with +1 +2 and even +3 which raise damage and armor.
It looks like greens and blues can drop anywhere the regular version of the item drops. I think the +'s can go up to +10. SWC
I usually have a plus on a white item? I haven't seen a blue and I didn't notice anything special about the greens. Of course I actually just became aware of the drops, didn't notice them at first. So with that in mind I probably just haven't noticed the things with the green.
I'm guessing drops are something like 10% green and 1% blue. Greens can give you things like "of strength" and "of power" and they usually bump up the damage / armor of the item. Blues are even better. The color convention isn't consistent. You can find a Fine Something +2 and it'll be white, even though it probably should be green. SWC
I find them pretty often. This is what I've found by the time I hit level 12 on my most recent character. I'm sure I've sold others. Just pick up everything, and always open chests. I like to get The Fool of Fortune as well. Not sure if it increases drops or just chests. Pickpocket is also handy. Try using it to steal from the couple in Custard Mansion, as well as any bosses or special enemies. Fire drakes also have a lot of nice stuff you can steal. At level 28 pickpocket enemies pretty much bleed items.
Can you have the special items like dagger of winter become 'fine dagger of winter +3' or something like that?
I think so. Not sure if all weapons allow it. I've found an elven darksword, nether impalers, venom daggers, and jewelry with options. I can't remember which of the other special stuff had options.