You can use two different types of colour swatches. You can paint drawings with vector swatches, which are the solid and gradient colours.
You can paint your vector drawings with bitmap texture swatches. You can import textures and add them to your palette. Textures must be *.psd or *.tga files. Transparency is supported. Once you have painted with textures, you can edit the gradient's position—see Using the Edit Gradient - Texture Tool.