Yes, you can.
Shaders and textures may change colour, lighting, or material effects, but they may not introduce new, clearly recognizable shapes.
Also the original shape must remain visually clear.
Example not allowed: Applying a brick texture where each brick is clearly a rectangle.
From the FAQ as extra:
- Transparency, Materials & Effects:
- Transparency, outlines, and visual effects (like glow, bloom or shaders) are allowed as long as they don't visually introduce new shapes or suggest forbidden ones.
- Particle systems must also use only the allowed shapes as individual particles and avoid arrangements that suggest forbidden shapes.
- Fog effects are allowed for subtle atmosphere, but they cannot form distinct or recognizable shapes.
- Materials are allowed, but shapes must remain clearly recognizable. Do not texture shapes to resemble other geometric forms.