A series of masks defining features of each mesh (cavities, edges, etc.) allow you to tweak the coloring of different parts of the rock:
I download your sample rock. And I must say it quite good. Well done. for me the bace textuer didnt realy match other objects I crating. But that was easy changed and I good resalt out of it.
Thanks WeekendWarrior! Any suggestions on what you’d like to see?
Ouch. My submission was rejected 
If you guys are still interested, you can get the pack at Necro’s Rock Box. Think I’m going to slink off and lick my wounds for a bit.
Did they say Why?
maybe invest in a rock pack on the marketplace to see what other people have done. I do think the textures could be improved, I like the way you set up the red dots on the rock,
Well, the gist was that all of the rocks were weird shapes not found in nature, which I disagree with (google Badlands rocks and you can see pretty much any rock shape imaginable). I can’t say it doesn’t sting a bit to be knocked out in the very first phase, when all they have is a couple of pictures (the same ones at the top of the thread right now). But it is what it is, and I learned a lot working on these.
Anyways, I’ll probably take a bit of a break and then start working on improving Necro’s Utility Material Pack. I’d like to improve some of the least useful materials (didn’t do much with the straw material originally), and add several new materials as well. A couple of the materials were done by making a mesh in Blender and baking the normals (the diamond plate and rubber mat materials). With ZBrush, I can really go in and detail them (add some wear in the grooves, for example). And I’d like to explore making materials from ZBrush sculpting.
I think you rocks… well… ehm, rock! But there are 6 rock packs on the marketplace. They can almost start a category called ‘rocks’. Perhaps that is a reason they rejected it, and to be fair I think it is good. Some diversity is needed.
Thanks Martin. I agree diversity is good, but choice and a variety in a particular category can be good too!
Perhaps you want to read this topic too: Top 3 most-submitted asset types, and top 3 opportunities - Marketplace - Unreal Engine Forums
It says rock submissions is in the top 3 of most submissions Epic receives.
I read that as rock materials rather than rock meshes. But I’m sure they probably get a lot of rocks too.
A second sample from the pack, for free: