An inventor – Tim Kehoe – spent 15 years and £2,000,000 developing the world’s first non-staining bubbles – he calls them zubbles!! See http://www.zubbles.com/
The bubbles contain a special dye that fades within 15 minutes of the bubble bursting. This is a clever use of a property of dyes – fading – that is usually thought of as a bad property and which scientists strive hard to eliminate. The special dyes developed for this product fade when exposed to air, light or pressure.
This reminds me somewhat of the breakfast cereal – cocopops – where the brown colorant in the cereal leaks out into the milk turning it a muddy brown colour. Not a nice thing – you might think. However, Kelloggs turned this into a marketing success with the phrase – “So chocolately it even turns the milk brown”. I’ve always thought this was very very clever. Very clever.