Go: package main

import (
	"fmt"
	"math"
	"strconv"
)

// ColorCode is a string like #rrggbb
type ColorCode string

// ColorName is a name of color
type ColorName string

// Color has colorname and colorcode
type Color struct {
	name ColorName
	code ColorCode
}

// ColorTable has default colors
type ColorTable struct {
	colors []Color
}

var (
	colorTable = ColorTable{
		[]Color{
			Color{"black", "#000000"},
			Color{"blue", "#0000ff"},
			Color{"lime", "#00ff00"},
			Color{"aqua", "#00ffff"},
			Color{"red", "#ff0000"},
			Color{"fuchsia", "#ff00ff"},
			Color{"yellow", "#ffff00"},
			Color{"white", "#ffffff"},
		},
	}
)

func main() {
	var code ColorCode
	fmt.Scanf("%s", &code)
	for {
		if code == "0" {
			break
		}
		name := colorTable.getNearestColor(code)
		fmt.Println(name)
		fmt.Scanf("%s", &code)
	}
}

func (colorstr ColorCode) parseColorValue() (float64, float64, float64) {
	rr, gg, bb := colorstr[1:3], colorstr[3:5], colorstr[5:7]
	rri, err1 := strconv.ParseUint(string(rr), 16, 8)
	ggi, err2 := strconv.ParseUint(string(gg), 16, 8)
	bbi, err3 := strconv.ParseUint(string(bb), 16, 8)
	if err1 != nil || err2 != nil || err3 != nil {
		err := fmt.Errorf(
			"Failed to read color strings, color code:%s, err: %v %v %v",
			colorstr, err1, err2, err3)
		panic(err)
	}
	return float64(rri), float64(ggi), float64(bbi)
}

func (table *ColorTable) getNearestColor(targetcode ColorCode) ColorName {
	var nearestColor ColorName
	var nearestValue = 1e5
	for _, v := range table.colors {
		trr, tgg, tbb := targetcode.parseColorValue()
		prr, pgg, pbb := v.code.parseColorValue()
		// diff := math.Sqrt(
		// 	math.Pow(prr-trr, 2) + math.Pow(pgg-tgg, 2) + math.Pow(pbb-tbb, 2))
		diff := math.Pow(prr-trr, 2) +
			math.Pow(pgg-tgg, 2) +
			math.Pow(pbb-tbb, 2)
		if nearestValue > diff {
			nearestValue = diff
			nearestColor = v.name
		}
	}
	return nearestColor
}

C++: #include "bits/stdc++.h"
#include<unordered_map>
#include<unordered_set>
#pragma warning(disable:4996)
using namespace std;
using ld = long double;
template<class T>
using Table = vector<vector<T>>;
const ld eps=1e-9;

//// < "D:\D_Download\Visual Studio 2015\Projects\programing_contest_c++\Debug\a.txt" > "D:\D_Download\Visual Studio 2015\Projects\programing_contest_c++\Debug\b.answer"
int main() {
	while (1) {
		string st; cin >> st;
		map<int, string>mp;
		mp[0] = "black";
		mp[1] = "blue";
		mp[2] = "lime";
		mp[3] = "aqua";
		mp[4] = "red";
		mp[5] = "fuchsia";
		mp[6] = "yellow";
		mp[7] = "white";
		if (st == "0")break;
		else {
			int red = stoi(st.substr(1, 2), nullptr, 16);
			int gre = stoi(st.substr(3, 2), nullptr, 16);
			int blu = stoi(st.substr(5, 2), nullptr, 16);
			int num = (red > 127) * 4 + (gre > 127) * 2 + (blu > 127);
			cout << mp[num] << endl;
		}
	}
	return 0;
}

C++: #include <iostream>
using namespace std;

const char* color[] = {
	"black", "blue", "lime", "aqua", "red", "fuchsia", "yellow", "white"
};

const int RGB[][ 3 ] = {
	{ 0, 0, 0 }, { 0, 0, 255 }, { 0, 255, 255 },
	{ 0, 255, 255 }, { 255, 0, 0 }, { 255, 0, 255 },
	{ 255, 255, 0 }, { 255, 255, 255 },
};

int xtod( char* c )
{
	int ret = 0;
	int mag = 16;
	for( int i = 0; i < 2; ++i, ++c ){
		int d = 0;
		if( *c >= '0' && *c <= '9' ){
			d = *c - '0';
		}else{
			d = *c - 'a' + 10;
		}
		ret += ( d * mag );
		mag /= 16;
	}
	return ret;
}

int distance( const int* o, int* x )
{
	int dd[ 3 ];
	for( int i = 0; i < 3; ++i ){
		dd[ i ] = x[ i ] - o[ i ];
		dd[ i ] *= dd[ i ];
	}
	return dd[ 0 ] + dd[ 1 ] + dd[ 2 ];
}

int main()
{
	char col[ 8 ];

	while( cin >> col && *col != '0' ){
		int n[ 3 ];
		for( int i = 0; i < 3; ++i ){
			n[ i ] = xtod( col + ( 1 + i * 2 ) );
		}
		int d[ 8 ];
		for( int i = 0; i < 8; ++i ){
			d[ i ] = distance( RGB[ i ], n );
		}
		int ans = 0;
		int ansD = 200000;
		for( int i = 0; i < 8; ++i ){
			if( d[ i ] < ansD ){
				ans = i;
				ansD = d[ i ];
			}
		}
		cout << color[ ans ] << endl;
	}

	return 0;
}

C++: #include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <ctime>
#include <iostream>
#include <algorithm>
#include <sstream>
#include <string>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <utility>
using namespace std;

#define rep(i,n) for(int (i)=0; (i)<(int)(n); ++(i))
#define foreach(c,i) for(__typeof((c).begin()) i=(c).begin();i!=(c).end();i++)

string in;
const string name[8] = {
  "black", "blue", "lime", "aqua", "red", "fuchsia", "yellow", "white"
};

bool is_digit(char c) { return '0' <= c && c <= '9'; }
int c2i(char c) { return c - '0'; }

string solve() {
  in.erase(0, 1);
  int my[3];
  rep (i,3) my[i] = 0;
  rep (i,3) {
    if (is_digit(in[i*2])) {
      my[i] = c2i(in[i*2]) * 16;
    } else {
      my[i] = (10 + (in[i*2] - 'a')) * 16;
    }
    
    if (is_digit(in[i*2+1])) {
      my[i] += c2i(in[i*2+1]);
    } else {
      my[i] += (10 + (in[i*2+1] - 'a'));
    }
  }
  
  double dk = double(1 << 28);
  int l = -1;
  rep (S,8) {
    int ar[3], temp = 0;
    for (int i = 2; i >= 0; --i) ar[i] = (S >> i & 1) ? 255 : 0 ;
    rep (i,3) {
      temp += (ar[i] - my[i]) * (ar[i] - my[i]);
    }
    double d = sqrt(double(temp));
    if (dk > d) {
      dk = d;
      l = S;
    }
  }
  return name[l];
}

int main() {
  while (cin >> in) {
    if (in == "0") break;
    cout << solve() << endl;
  }
  return 0;
}

C++: #include <cstdio>
#include <iostream>
#include <cmath>
#include <cstdlib>
using namespace std;
string color[] = {"black", "blue", "lime", "aqua",
    "red", "fuchsia", "yellow", "white"};
int nums[][3] = {{0,0,0}, {0,0,255}, {0,255,0}, {0,255,255},
    {255,0,0}, {255,0,255}, {255,255,0}, {255,255,255}};

int convert(string str) {
    int res = 0;
    if ('0'<=str[0]&&str[0]<='9') {
        res += (str[0]-'0') * 16;
    } else if ('a'<=str[0]&&str[0]<='f') {
        res += (str[0]-'a'+10) * 16;
    }
    if ('0'<=str[1]&&str[1]<='9') {
        res += (str[1]-'0');
    } else if ('a'<=str[1]&&str[1]<='f') {
        res += (str[1]-'a'+10);
    }
    return res;
}

int main() {
    string str;
    while (cin >> str) {
        if (str == "0") break;
        double d = 10000000.0;
        string res;
        int r = convert(str.substr(1,2)), g = convert(str.substr(3,2)), b = convert(str.substr(5,2));
        for (int i=0; i<8; i++) {
            double tmp = sqrt(pow(r-nums[i][0], 2)+pow(g-nums[i][1], 2)+pow(b-nums[i][2], 2));
            if (tmp < d) {
                d = tmp;
                res = color[i];
            }
        }
        cout << res << endl;
    }
}