Making the colour map
Even though the instruction for making the procedural map and baking the map and use it for painting are max specific, I'm sure you can apply these techniques to other packages because of the nature of procedurals and simply because most of the surface editors in other packages have the noise and cloud/smoke procedural maps already included in them.
You may be asking yourself why are we going to make a procedural map instead of just taking a screen shot of the unwrapping editor? Simply because making a procedural map and then baking them it is a good way to insure that the edges of the object will blend together seamlessly and a procedural map could also provide us with a good initial base color that we could use as reference when painting details in photoshop.
To start off open the scene file included in the leaf zip file, you should see the fully unwrapped leaf model ready to be painted, but instead of taking a screenshot of the uv unwrap modifier were going to create a simple procedural texture and then bake it, as I mentioned before this way we ensure we start off with a seamless texture and some colors we can use as reference for painting as well.
Open the material editor and ad a smoke map to the diffuse channel of a new material, change the size to 10, give color 1 an rgb value of R:101 G:54 B:16 and give color 2 a value of R:81 Green:36 Blue:0, this will produce a brown tone witch is part of the discolored areas in our leaf.
Add the current smoke map to a noise by clicking on the smoke button and picking noise from the material/map browser (keep old map as sub-map), change the type to fractal, in the noise threshold give the high parameter a value of 0.6 and a low value of 0.25, and add another smoke map to the empty color 2 slot.
This time instead of browns were going to use yellow tones to add more variation to the faded areas in the leaf, change the size to 10 give the color 1 an rgb value of R:167 G:128 B:22 and color 2 a value of R:196 G:161 B:22.
Click the go to parent button once to go to the noise base level and add the noise map to another noise map by clicking at the noise button and picking noise from the material/map browser and keep old map as sub-map in order to create the third color layer, in the new noise map change the type to fractal, size to 30, noise threshold high value of 0.6 and low value of 0.25, phase to 10 just to give it a different pattern, and click the swap button in order for our old noise map to move to the second color slot.
Add another smoke map to the empty color channel (first color slot), change the size for that smoke map to 10, give color 1 a value of R:44 G:60 B:0 and color 2 a value of R:67 G:84 B:0
We're finished with this step, for now make a quick render of your scene, if you're not entirely happy with the pattern or color feel free to adjust the maps to your liking before moving to the next steps.