Think of rhyolite like a shaken soda can that foams over when you open it, rhyolite is volcanic foam that is rich in silica. Many rhyolites contain other crystals such as topaz, beryl, bixbyite etc. In the field form which this slab was taken, many of the rocks have tiny black specs in them, they were tiny crystals of bixbyite.
When one sees a rhyolite with alternating black and white bands (or light/dark streaking), it’s typically due to flow banding or compositional banding. Here’s how that comes about:

• Flow banding: As viscous rhyolitic lava moves (flows), internal shear and friction against its boundaries cause the magma to deform and stretch. Particles, phenocrysts, or vesicles may be dragged into streaks or bands.

• The bands often represent variations in mineral content, crystal concentration, vesicle content, or glass vs microcrystalline material. Lighter bands may be richer in quartz/feldspar, whereas darker bands may have more mafic minerals, glass, or residual melt.

Thus, “black-and-white” banded rhyolite is a rhyolite where the banding contrast is strong, perhaps due to high variation in composition or presence of dark inclusions (e.g. glass, mafic minerals) alternating with pale, silica-rich material.