Here is an example how to tweak the image with a custom script in case of volcano eruption:
return [ B04*2.5 + Math.max(0,B12-0.1), B03*2.5 + Math.max(0,B11-0.1), B02*2.5];
Etna volcano eruption, dated 16. 3. 2017. Image combined from true colour image, overlaid with SWIR bands 11 and 12. (view on Sentinel Playground)
You can find more examples and how to tweak the images for easier detection of Earth surface changes, clouds, snow, shadow, water etc. in our blog post.