I don't think there ever was a Dark Dirt that came with the base caw textures. If you go to your Programs Caw folder, you'll see all the base textures. You can copy and paste any you've missplaced into your Documents Caw folder.

Programs(x86)
Electronic Arts
The Sims 3 Create a World
UserToolData
SourceTextures

HystericalParoxysm has a set with dirt_dark. It's available for download on post #16 of this thread, and Martine's has a Dirt_Dark_Base

My bad, I meant it comes as an in-game terrain paint. There is a light dirt and a dark dirt. I'm aiming to use textures that are already in the game so I can match them up on individual lots. I've already got the Light Dirt in my CAW files, but the file listed as Dark Dirt in Martine's pack doesn't seem to be the same one as the in-game one. I would try extracting it myself, but S3OC won't open.

Ooohh no! Silly me! It is the right texture . Thanks for your help anyway

Haha sorry to be a pain. I'm having another problem with the dark dirt -when using a round brush with a low opacity and falloff, all the other textures work and can be blended nicely, the dark dirt seems to have a jagged edge even with low falloff, and the opacity must be set high or it does not work at all, making it impossible to blend. Any idea why this is or how it can be fixed?

Where you add your texture in the list effects the way it reacts with the other textures. I like to add them in clusters from either dark to light, or vice-verse, depending on the effect I want.

Example Pallette:
Dark rock
Light Rock
Dark Dirt
Light Dirt
Light Grass
Medium Grass
Dark Grass


Also you can save the texture with a different setting. Most of Martines textures are saved as a DXT5 (Interpolated Alpha) which gives it a more transparent appearance, and it usually blends better. You can do a "save as" in a paint program, I use Paint.net, and save it as a DXT1 (Opaque/1-bit Alpha) and see if that helps.

You're amazing! It has the effect I was after now.
If the texture order has impact on the way they react with each other, is there any way to edit the order, without having to delete existing layers, after you've already started painting?

If you've already started painting, I would just stick with the way it is. I've tried deleting one in the center, then all the textures under it got wonky. It's not that big of deal, it just works a bit better for me, and how I paint.

Wow thank you so much, everyone! This makes the terrain on my map look much better than it does with the default textures.