A former Google X hardware engineer created a system called Spectrum that mixes red, yellow, blue, and white paints from off-the-shelf pressurized cans to produce custom hues in real time. (https://spectrum.ieee.org/spray-paint-color-creator) Initial solenoid valve prototypes failed due to backflow from pressure differences between cans, leading to a sequential pulsing approach where only one valve opens at a time and turbulence handles mixing. The inventor settled on pulse durations between 30 and 250 milliseconds with 1-millimeter tubing after extensive testing.

The solution required inventing a high-speed rotary pinch valve using a stepper motor, rolling bearing, and spring to constrict flexible tubing, preventing clogging and leaks even when disconnected. (https://spectrum.ieee.org/spray-paint-color-creator) This normally closed valve cycles in tens of milliseconds and integrates with an Arduino Nano, knobs, display, and force-sensitive button for color selection and gradients.

The 3D-printed DIY system creates up to 4,096 distinct colors though fewer unique hues due to ratio multiples, with project files and videos at https://www.sandeshmanik.com/projects/spectrum and technical preprints on TechRxiv. (https://spectrum.ieee.org/spray-paint-color-creator)