Holi color catcher on an Arduino Uno

// Holi color catcher: hold anything colorful to the sensor, a flower, a shirt,
// a pinch of colored powder in a clear bag, and the strip catches its color,
// names it and keeps it in a row of the last eight colors you caught.
//
//   TCS34725  SDA -> A4, SCL -> A5, VIN -> 5 V, GND -> GND
//   palette   8 WS2812B LEDs, DIN <- 330 ohms <- pin 6
//
// The TCS34725 measures red, green, blue and clear light through four sets of
// filtered photodiodes, lit by its own white LED. The sketch turns the three
// colors into shares of their total, so a dim red and a bright red both read
// as red, and picks the nearest name from a short list.
//
// A new color is caught only when it is different from the last one and the
// sensor sees something close (the clear count is high), so holding one thing
// still catches it once, not over and over.
//
// Things to try. Change the color in front of the sensor. Add a color to
// NAMES with its red, green and blue shares in thousandths.

#include <Wire.h>
#include "Adafruit_TCS34725.h"
#include <Adafruit_NeoPixel.h>

const int LEDS = 8;
const uint16_t NOTHING_BELOW = 1500;   // clear count with nothing close

Adafruit_TCS34725 tcs = Adafruit_TCS34725(TCS34725_INTEGRATIONTIME_50MS, TCS34725_GAIN_4X);
Adafruit_NeoPixel palette(LEDS, 6, NEO_GRB + NEO_KHZ800);

struct Shade {
  const char *name;
  uint16_t red, green, blue;   // shares of the total, in thousandths
  uint32_t show;               // what the strip shows for it
};
const Shade NAMES[] = {
  {"red", 650, 200, 150, 0xFF0000},
  {"orange", 560, 340, 100, 0xFF6000},
  {"yellow", 470, 430, 100, 0xFFC000},
  {"green", 200, 520, 280, 0x00D040},
  {"blue", 140, 310, 550, 0x0040FF},
  {"purple", 330, 240, 430, 0x9000FF},
  {"pink", 480, 220, 300, 0xFF2080},
};
const int COUNT = sizeof(NAMES) / sizeof(NAMES[0]);

int last = -1;
int caught = 0;
uint32_t row[LEDS];   // the colors caught, newest first

int nearest(uint16_t r, uint16_t g, uint16_t b) {
  uint32_t total = (uint32_t)r + g + b;
  if (total == 0) return -1;
  long rs = (uint32_t)r * 1000 / total, gs = (uint32_t)g * 1000 / total, bs = (uint32_t)b * 1000 / total;
  int best = 0;
  long bestDistance = 0x7FFFFFFF;
  for (int i = 0; i < COUNT; i++) {
    long dr = rs - NAMES[i].red, dg = gs - NAMES[i].green, db = bs - NAMES[i].blue;
    long d = dr * dr + dg * dg + db * db;
    if (d < bestDistance) {
      bestDistance = d;
      best = i;
    }
  }
  return best;
}

void setup() {
  Serial.begin(9600);
  palette.begin();
  palette.setBrightness(150);
  palette.show();
  if (!tcs.begin()) {
    Serial.println("No TCS34725 found: check SDA and SCL");
    while (1) delay(10);
  }
  Serial.println("Color catcher ready: hold something colorful to the sensor");
}

void loop() {
  uint16_t r, g, b, c;
  tcs.getRawData(&r, &g, &b, &c);
  if (c < NOTHING_BELOW) {
    last = -1;   // nothing there: the next color counts as new
    delay(100);
    return;
  }
  int shade = nearest(r, g, b);
  if (shade < 0 || shade == last) {
    delay(100);
    return;
  }
  last = shade;
  caught++;
  // Slide the row along and put the new color first.
  for (int i = LEDS - 1; i > 0; i--) row[i] = row[i - 1];
  row[0] = NAMES[shade].show;
  for (int i = 0; i < LEDS; i++) palette.setPixelColor(i, row[i]);
  palette.show();
  Serial.print("Caught ");
  Serial.print(NAMES[shade].name);
  Serial.print(", color ");
  Serial.println(caught);
  delay(100);
}