This instrument uses RGB LEDs to
illuminate the tested surface and plays tones depending on
key is pressed, it plays the tone (about 200 ms), with lower
pitch if the red component is darker, and higher pitch if it is
lighter. The same is for green and blue, so the whole sequence
is about 600 ms. After that, if the momentary key is still ON,
MCU goes to sleep mode, to save battery. The key simply switches
power supply ON and OFF.
This instrument helps blind
persons or daltonists to get more information about their
surrounding. After some time they will not listen the tone
pitches, but the "melody" of the colour.
The lower part of the inside
surface of the enclosure must be black, and the photo transistor
light shielded (with the black heat shrinkable tube or so), to
ignore direct light from LEDs and to pick only the reflected
light from the tested surface.
Here's the schematics...:
...and YouTube demo: