So after patch 2.0.1. all items have stats split in to the primary and secondary groups and some of them are marked with orange diamond.
What is the logic behind this? It seems too random.
Before 2.0.1. the problem with item drops was that some items would get all combat useful stats like damage, health, crit, etc. making them a much better choice than some items that would get just support things like move speed, pickup radius, gold find, etc. Items that got half of both should have been ideal for game but were still underpowered compared to those with all combat useful stats.
To fix this Blizzard decided to split item stats in 2 groups(Primary and Secondary) and divide them in 4:2 or 3:3 ratio on all items, so now every item will contribute something to your combat power and will have some support skills.
Primary group combat useful stats like: core attributes, armor, critical chance and damage, health regen, splash damage, etc.
Secondary group support stats that help you in other ways like: movement speed, pickup radius, single resist, resource gain, experience gain, magic find, etc.
Longer list here.
When you compare 2 items the game will calculate difference between your Damage, Toughness and Healing that would occur if you equip the targeted item.
Orange diamond next to some stats means that those stats are not included in the comparison calculation (they don’t affect your Damage, Toughness or healing), and you will have to decide for yourself if they are worth changing the item.