Will we be able to create our own custom NCP's in the furture ?

You can actually do this now.   Check the modding forums.  Basically, if you design a sovereign in the custom sovereign interface you can then change it into an NPC to be recruited/hired by the factions.    It actually very simple to do.

2nd - Colors can definitely be changed.  Check out the metal color option in the modding faction editor: https://forums.elementalgame.com/390184.   You can create a new faction and have all the colors customized how you would like.   It does seem like leather is set to brown however, and no one has yet changed the colors of mounts (that would require a new skin), but the things you are looking for are not that far from reality.  

Yes, this is actually pretty easy. As Murteas said, just make them in sovereign creator then modify their XML file and add/edit this:

        <IsSovereign>0</IsSovereign>
        <!-- New NPC Champion Data -->
        <Class>Thief</Class>
        <SpawnRating>1</SpawnRating>
        <NPCSpawnLikelihood>400</NPCSpawnLikelihood>
        <NPCTalentValue>1</NPCTalentValue>
        <NPCRecruitmentText>Hello, you can hire me for %d gildar, if you'd like.</NPCRecruitmentText>
        <Rumor>There are rumors of a well-to-do thief for hire around %s.</Rumor>
        <MountedAnimationPack>MountedSoldierAnimationPack</MountedAnimationPack>

The important code for making them recruit-able is outlined in yellow. Good luck!

You can change mount colours justfind mounts in the core files, copy and paste it into a new XML wordpad doc like you would with a new item, then adjust the colour numbers to whatever colour you like. I have red fire wargs as a new mount.

Thanks so much for this information!  I would love to create a custom NPC (or several).  Can the created NPC have essence, out of curiosity?  How is the cost of recruiting determined?  Can the class name be custom?

No problem. Yes, they can have essence.

I believe it is determined by the talent, their level, equipment, and, possibly, based on their stats and skills (more = more expensive).

I honestly don't know what <class> does. I think you can make it whatever you want. If you want a unique history or profession then you'd need to make that from another file SovereignTalents.XML. If you want the character to display a unique title then you'd need to modify the <DisplayName> to something unique and change the <UnitDisplayName> to the character's name. It makes the card a little more unique looking and still retains the character's correct name.

Here are some more fun codes to play with:

        <DisplayName>Thief</DisplayName>
        <Description>A thief of thieves, this character likes to rob the robbers and return to the wealthy so he can make legitimate money stealing.</Description>
        <UnitDisplayName>Josh</UnitDisplayName>

        <SoundPack>Soundpack_OldWizard1</SoundPack>

Lastly, you can remove the medallion code and the game will automatically generate the character a new one. If you update the character's look then I'd suggest doing this. Also, you can link the character's medallion to any image you want and it'll display ingame (ie. Boulders Gate portraits).

Personally, I enjoy making heroes and find all this fascinating.

I hope that a lot of the modding will be available in the workshop, I don't mind doing the line changes but I would like to create a new npc the same way I can create a new sovereign. I guess I'm into more of playing the game than modding for it.