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 <iostream>
#include <cctype>

using namespace std;

string Strength[8] = {"000000","0000ff","00ff00","00ffff",
		      "ff0000","ff00ff","ffff00","ffffff"};

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

int x_t(char c){
  if(islower(c)) return 10 + (c - 'a');
  return c - '0';
}

int change(string s){
  return x_t(s[0])*16 + x_t(s[1]);
}

string solve(string R,string G,string B){
  int pos,Min = (1<<29),d;
  int r = change(R),g = change(G),b = change(B);
  string rr,gg,bb;

  for(int i = 0 ; i < 8 ; i++){
    rr = Strength[i].substr(0,2);
    gg = Strength[i].substr(2,2);
    bb = Strength[i].substr(4,2);
 
    int rk = change(rr) ,gk = change(gg) ,bk = change(bb);    
    d = (r-rk)*(r-rk) + (g-gk)*(g-gk) + (b-bk)*(b-bk);

    if(d < Min){
      Min = d;
      pos = i;
    }
  }

  return Color[pos];
}

int main(){
  string str;

  while(cin >> str ,str != "0"){
    string R,G,B;

    R = str.substr(1,2);
    G = str.substr(3,2);
    B = str.substr(5,2);

    cout << solve(R,G,B) << endl;
  }

  return 0;
}

C++: #include <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <cmath>
#include <stack>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <list>
#include <iostream>
#include <sstream>
#include <climits>
#include <cfloat>
#include <complex>

using namespace std;

int main()
{
	char* colors[] = { "black", "blue", "lime", "aqua"
		, "red", "fuchsia", "yellow", "white" };
	char buf[16];
	while (cin.getline(buf, sizeof(buf)), *buf != '0')
	{
		int r, g, b;
		sscanf(buf, "#%2x%2x%2x", &r, &g, &b);
		char* ans;
		double mind = 1e10;
		for (int i = 0; i < 8; ++i)
		{
			double rr = (i >> 2 & 1) * 0xff;
			double gg = (i >> 1 & 1) * 0xff;
			double bb = (i & 1) * 0xff;
			double d = sqrt((rr-r)*(rr-r) + (gg-g)*(gg-g) + (bb-b)*(bb-b));
			if (d < mind)
			{
				mind = d;
				ans = colors[i];
			}
		}
		puts(ans);
	}

	return 0;
}

C++: #include<iostream>
#include<string>
using namespace std;
 
const int INF = 10000000;
 
int base16(char c) {
  if( 'a' <= c ) return c-'a'+10;
  else return c-'0';
}
 
int main() {
 
  string s;
 
  int coltabel[8][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 } };
 
  string nametable[8] = { "black", "blue", "lime", "aqua",
             "red", "fuchsia", "yellow", "white" };
 
  while(true) {
 
    cin>>s;
    if( s=="0" ) break;
 
    int r,g,b;
    r = base16(s[1])*16+base16(s[2]);
    g = base16(s[3])*16+base16(s[4]);
    b = base16(s[5])*16+base16(s[6]);
 
    int res,tmp=INF,t;
 
    for(int i=0; i<8; i++) {
      if( ( t = (r-coltabel[i][0])*(r-coltabel[i][0])
      + (g-coltabel[i][1])*(g-coltabel[i][1])
      + (b-coltabel[i][2])*(b-coltabel[i][2]) )
      < tmp ) {
    //cout<<t<<" "<<i<<endl;
    res = i;
    tmp = t;
      }
    }
 
    cout<<nametable[res]<<endl;
  }
}

C++: #include<bits/stdc++.h>
using namespace std;
int main()
{
    string color[]={"black","blue","lime","aqua","red","fuchsia","yellow","white"};
    int colornum[8][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 value[200]={};
    for(int i=0;i<10;i++)value['0'+i]=i;
    for(int i=0;i<6;i++)value['a'+i]=10+i;
    string str;
    while(cin>>str&&str!="0"){
        int num[3];
        for(int i=0;i<3;i++)num[i]=value[str[1+2*i]]*16+value[str[2+2*i]];
        int ans[8]={};
        for(int i=0;i<8;i++){
            for(int j=0;j<3;j++)ans[i]+=pow(colornum[i][j]-num[j],2);
        }
        int co=0;
        for(int i=1;i<8;i++)if(ans[co]>ans[i])co=i;
        cout<<color[co]<<endl;
    }
}

C++: //41
#include<iostream>
#include<cstdlib>

#define S(X) ((X)*(X))

using namespace std;

int main(){
  for(char c[8];cin>>c,c[0]!='0';){
    int md=1<<30;
    int cn;
    unsigned cd=strtoul(c+1,0,16);
    for(int i=0;i<8;i++){
      unsigned d=0;
      for(int j=0;j<3;j++){
	static const unsigned cc[]={0x0,0xff,0xff00,0xffff,0xff0000,0xff00ff,0xffff00,0xffffff};
	d+=S((cd>>j*8&0xFF)-(cc[i]>>j*8&0xFF));
      }
      if(d<md){
	md=d;
	cn=i;
      }
    }
    const char *cstr[]={"black","blue","lime","aqua","red","fuchsia","yellow","white"};
    cout<<cstr[cn]<<endl;
  }
  return 0;
}

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

string s;
string color() {
	char l[6];
	for (int i = 0; i < 6; i++) {
		l[i] = s[i + 1];
	}
	int r, g, b;
	int z[6];
	for (int i = 0; i < 6; i++) {
		if (l[i] == '0') {
			z[i] = 0;
		}
		else if (l[i] == '1') {
			z[i] = 1;
		}
		else if (l[i] == '2') {
			z[i] = 2;
		}
		else if (l[i] == '3') {
			z[i] = 3;
		}
		else if (l[i] == '4') {
			z[i] = 4;
		}
		else if (l[i] == '5') {
			z[i] = 5;
		}
		else if (l[i] == '6') {
			z[i] = 6;
		}
		else if (l[i] == '7') {
			z[i] = 7;
		}
		else if (l[i] == '8') {
			z[i] = 8;
		}
		else if (l[i] == '9') {
			z[i] = 9;
		}
		else if (l[i] == 'a') {
			z[i] = 10;
		}
		else if (l[i] == 'b') {
			z[i] = 11;
		}
		else if (l[i] == 'c') {
			z[i] = 12;
		}
		else if (l[i] == 'd') {
			z[i] = 13;
		}
		else if (l[i] == 'e') {
			z[i] = 14;
		}
		else if (l[i] == 'f') {
			z[i] = 15;
		}
	}
	r = z[0] * 16 + z[1];
	g = z[2] * 16 + z[3];
	b = z[4] * 16 + z[5];
	if (r <= 128) {
		if (g <= 128) {
			if (b <= 128) {
				return "black";
			}
			else {
				return "blue";
			}
		}
		else {
			if (b <= 128) {
				return "lime";
			}
			else {
				return "aqua";
			}
		}
	}
	else {
		if (g <= 128) {
			if (b <= 128) {
				return "red";
			}
			else {
				return "fuchsia";
			}
		}
		else {
			if (b <= 128) {
				return "yellow";
			}
			else{
				return "white";
			}
		}
	}
}

int main() {
	string g[1001];
	int x;
	for (int i = 0;; i++){
		cin >> s;
		if (s == "0") {
			x = i;
			break;
		}
		g[i] = color();
	}
	for (int i = 0; i < x; i++){
		cout << g[i] << endl;
	}
	return 0;
}