Kikko - Kikko armor consists of a clever arrangement of hexagonal plates made from iron and sewn to cloth, granting the wearer greater flexibility than that provided by many armors that afford similar defense. The plates may be left exposed or hidden by a layer of cloth.
Darkleaf - Items not primarily constructed of leather, fur, or hide are not meaningfully affected by being partially made of darkleaf cloth. As such, padded armor, leather armor, studded leather armor, and hide armor can be made out of darkleaf cloth (although other types of armor made of leather or hide might be possible). Because darkleaf cloth remains flexible, it cannot be used to construct rigid items such as shields or metal armors. Armors fashioned from darkleaf cloth are always masterwork items; the masterwork cost is included in the listed prices.
I would assume that a kikko contains more metal than studded leather armour. One of the purposes of a kikko is listed as allowing more fleibility, which is one of the advantages of darkleaf cloth. So, could a kikko be made of darkleaf cloth or not?
You answered your own question via the bolded parts. The protective subject are metal plates that are kept together with cloth. It may also be covered with cloth (but not always), and neither cloth components are really mentioned in, or considered crucial to the protectiveness that the Kikko provides. Even if it is, it's certainly not constructed on a primary level, so if you used Darkleaf Cloth, it would not have any mechanical impact on your armor.
That being said, Kikko is Medium armor, and Mithril will have a better impact than Darkleaf Cloth, so...
No, it's primarily metal, unlike studded leather which is primarily leather. It can be made of Mithral, which is well worth the cost, as it produces effectively light armor with no ACP and a max dex of +6. This can be worn by bards, rogues, and magi, even though they aren't proficient, as it has no ACP and therefore causes no penalty to be applied to attack rolls for nonproficiency. It also has only 10% ASF chance, which can be negated by Arcane armor training.
Kikko sounds closer to scalemail or coinmail than studded leather, while coinmail is no longer official neither is leather scalemail, which you might consider using. I think they are both somewhere in 3.5.
The scales in scalemail can be hexagonal in shape.
(I don't think "coinmail" is a real word, I think it's actually scalemail-coin or coin scalemail or something, but "coinmail" works to help visualize it.)