Changing the Default Material

From ZBrush Info

To change the default MatCap Red Wax material, first save the material you wish to use to disk. This can be a custom modified material or one of the standard startup materials. Give the file a suitable name to distinguish it from other materials.

Select the default MatCap Red Wax material or set the Material Palette Item Info slider to 1. Now press the Load button and select the material you previously saved to disk. It will load into the palette, replacing the MatCap Red Wax material.

Simply loading a material will not make it the default for future ZBrush sessions. To ensure that it loads every time it must be saved as part of the startup document. Select the SimpleBrush from the Tool palette. Make sure the M or MRGB button is on (so that material is painted) in the Draw Palette, ZAdd is on, and that your material is still selected. Paint a few strokes on the canvas. They need only be small, for example in a top corner; as long as a material is painted on the canvas it will be saved with the document. Now press the Save As button in the Document Palette and save the document as StartupDocument.zbr in the ZBrush3\ZStartup folder. Your new default material will now load on startup.

To Learn About The Startup Document Click Here.