Price ranges for the different weopem colours

stats for one, next is how rare is it? a crappy blue crystalline can fetch a high price, just because its so rare.
one thing that dictates is the skin(art) of the item. if that particular skin drops rarely, its more valuable than a regular common one with the same stats.

most popular damage mods seem to be %>50%, and % while enchanted. so those are usually more sought after than lets say % while hexed.

sometimes popularity of particular mods is dependant on FOTM, as certain builds become popular.....

perfection, usually the most valuable of any particular item, is a perfect gold, with perfect(popular) mods. EX; 15%>50% req8 +30hp 10/10 sundering.

look at the weapon mod baseline pricing thread, give you an idea of which mods are more sought after.

Very well said treserious... Also remember that Gold items typically have more than a mod. Ususally they have an added damage or something similar. Treserious addressed this, but I think you have to look at the differences too.

Let's use a max damage longsword (common skin)

White item 15-22 dmg

Light Blue item 15 -22 dmg +might have 1 mod or added dmg but not a sure thing

Purple item 15-22 with USUALLY one or two mods

Gold Item 15-22 with usually 2 mods and a dmg bonus

There is a heck of a difference in price between a white 15-22 Longsword and a Gold 15-22 longsword with 10/10 Sundering and +30 health and 15% extra dmg over 50% health.

The white would sell to merchant for 150 gold. The Gold would fetch well over 500k I would imagine.

That longsword is 300k at most, unless its req 7 ^^^

like Greygon said, whites have no mod, blue sometimes have one, or "precious/highly salvageable", purples have 1 or 2 mods, often stupid or useless ones, sometimes decent damage mods.
golds however have the highest chance at having 2-3 mods, and more often than not, a damage mod, at least melee weapons, and bows do.

for example, back to the longsword.

sundering longsword of fortitude.-(the name says it all, has sundering, is a longsword, and gives more health)
damage 15-22(req 8)-lower the requirement, the better, the best are 7-8, while still maintaining max damage for that particular weapon type
+15% damage(while health is above 50%)-this is the innate mod of the weapon, cannot be changed)
10/10 sundering
+30 health

with a weapon, the first part of the name, indicates a hilt, haft, string mod, and staff heads sundering in our example. this can include the 4 elements, vampiric, zealous, furious, poisoning, barbed, cruel

the last one indicates grips for axes hammers and bows, and pommel for swords, and staff wrapping for staves. this is the health mod, armor mod(vs everything max+5, vs elements max+7, vs physical max+7) + % to length of enchantments, +1 to particular attribute % chance etc

the types of innate mods for melee weapons and bows can be the following
+ % damage while health above 50%(max 15%)
+ % damage while health below 50%(max 20%)
+ % damage while enchanted(max 15%)
+ % damage while in a stance(max 15%)
+ % damage while hexed(max 20%)
+ % damage while foe is hexed(max 20%)

for staves, rods, offhands, and sheilds are different, staves do not have damage mods, and rods and sheilds and offhands do not have interchangeable mods.

staves innate mods can include
faster recharge
faster casting
this is usually up to 10% chance unless it specifies an attribute, then it could be up to 20%chance.

sheilds, can have the following popular mods
+ hp, max 30 without condition requirement, or +45 while enchanted, in a stance, hexed etc.
and -1, 2, 3 damage, also often dependant on a requirement as stated above.

many items i have seen also can have + % damage vs specific creatures( trollslaying, giant slaying, deathbane, pruning, etc) for weapons
and defence against the same creature types.(+7 armor vs dwarves, etc)on shields and offhand items.
i had a sword for a while that was +20% vs undead, came in handy for farming GoK, and that area in FoW.
i still have a +20%vs dwarves mod on a bow i use in GF and SF

there are many other innate mods out there, and weapon mods, this is just to give you an idea

so, the value of items is determined by the stats, and the look/rarity of the item, and is usually dependant on popularity at the time. just remember, the higher the stat, the better, unless its the req.