Pairs of contrasting threads twining around each other on a background of interlinking can create a range of patterns.
Inspired by Ancient Designs
These designs were inspired by hairnets found in Egypt, dating to the 4th-8th centuries. Carol James has charted and reproduced many of these colorful motifs and periodically teaches a short online course on twining. See her current teaching schedule here.
One of my favorite projects while demonstrating sprang is to start with a warp with every 5th loop a different color and gradually twine those loops towards the center until they join into a tree. I've found the random pattern is easier when my brain is distracted by talking with others so I'm not thinking too hard about whether the branch flares outward or returns toward the middle.