Thank you Travis.
I will definitely be using that technique. Selective color (in photoshop) will help me isolate color moves to the shadows as well. I will be using all your tips.
However, I'm now back to the modeling challenge.
1. If i use something like the "stone placement" script. It only gets me so far. I have made a 12"x12" section of stone (3 bricks wide by six bricks high). I then go in and change the settings of the modifiers (to obtain the required look). But this makes crazy detail thats too much to render. With just a small section of bricks (about a 12"x120" area) I have more than 20 million faces. I need an area thats 40"x120".
I would probably go this route but the displacement on the bricks is rough on all sides. I need smooth on all sides except the ones exposed. But if i want displacement only on one face, i think i need to make each brick individually. Thats approximately 500 bricks.
2. I can use another script which will make a bunch of boxes for me the right size, and pattern. But very clean edges. Maybe too clean. However, I can then make a bunch of bitmap images (hopefully only 100 unique bitmap images) and map them. However, i think there will be too much repetition. And i still have the challenge of trying to make a natural edge for each of these boxes.
If it was just five bricks i can do it easily without asking all these questions. But with approximately 500 bricks, its a completely different story.
Anyway, i won't bore everyone. I'll keep my posts to a minimum so when I'm in real trouble, you guys won't be sick of me.