Here is a guide of armor inlastchaos.5finggers edited it and I post it here.

The level 75-77 armor is different from previous armor for all the classes. The first is that while you could equip a piece of armor 5 levels above you, with this new level you must be that level to equip it. For example, at level 65, you can equip the level 70 gloves. But with this new level, you must be level 75 to equip the level 75 gloves. So any armor from level 75 to level 127 is equipped to the character of the same level.

There are 4 colors of armor - White, Yellow, Green, and Blue, with White being the lowest armor and last chaos gold being the highest armor.

White Named Armor - Usually sold to NPC. But you could go to transmuter and use for smelts. Only plain armor can be smelted. The level 95-97 armor with white 4 seals, sometimes you can sell in the trader as these levels of armor are extremely rare, as you will find out when you get to that level.
Yellow Named Armor - Sometimes if you get good seals, you can sell these. Shop around to see what else is selling.
Green Named Armor - Most of the time with at least 4 seals, it is possible to sell. At high levels like 90x armor, even a 3 green seal can sell.
Blue Named Armor - Most of the time with at least 4 seals, it is possible to sell. This type of armor carries the 6th seal. A piece of armor may have 4 regular seals, and the 6th seal also. With experience you will find that some 6th seals are overpriced and not really of any help much, as the anti-stun.

You must be knowledgeable of the seals if you wanna buy armors. For Example, two evasion sets are the same except for the 4th seal. One has evasion 56 and the other has Swiftness of Reflexes 16. Basically, what is good to know that for a knight, it is about 10 points of reflex to equal 1 evasion. So in the long run, you would want to go with the evasion as the 4th seal. Seals are mixed and just last chaos gold of knowing what you want.

You must be the same level starts at Level 75 when you take the armor. It jumps to level 85, level 95, level 105, and 115. Be aware of the blood seals. So G4 and Y4 armor have the same stats but just a slight difference on the defense. It is just that the g4 armor can also be found in the G5 also. I used 65 armor and skipped level 70 armor, to save up for the level 75 armor.