The following JavaScript code when added to a web page allow someone to convert RGB colors to the appropriate HEX code. 
 
<!-- TWO STEPS TO INSTALL HEX-RGB CONVERTER: 
 
  1.  Copy the coding into the HEAD of your HTML document 
  2.  Add the last code into the BODY of your HTML document  --> 
 
<!-- STEP ONE: Paste this code into the HEAD of your HTML document  --> 
 
<HEAD> 
 
<SCRIPT LANGUAGE="JavaScript"> 
<!-- Original:  Ryan Sokol --> 
<!-- Web Site:  http://www.logicode.net --> 
 
<!-- This script and many more are available free online at --> 
<!-- The JavaScript Source!! http://javascript.internet.com --> 
 
<!-- Begin 
function NumToHex(num1,num2) { 
strNum=document.forms[0].elements[num1].value; 
for(i = 0; i < strNum.length; i++) { 
chr=strNum.substring(i, i + 1);		 
if((isNaN(chr))||(chr == ' ')) { 
alert('You must enter a digit between 0 and 9!'); 
document.forms[0].elements[num1].select(); 
document.forms[0].elements[num2].value=''; 
return false; 
   } 
} 
if(strNum > 255) { 
alert('You must enter a number between 0 and 255!'); 
document.forms[0].elements[num1].select(); 
document.forms[0].elements[num2].value=''; 
return false; 
} 
else { 
base = strNum / 16; 
rem = strNum % 16; 
base = base - (rem / 16); 
baseS = MakeHex(base); 
remS = MakeHex(rem); 
document.forms[0].elements[num2].value=baseS + '' + remS; 
ChangeBackground(3, 4, 5); 
return true; 
   } 
} 
function MakeHex(x) { 
if((x >= 0) && (x <= 9)) 
return x; 
else { 
switch(x) { 
case 10: return "A";  
case 11: return "B";   
case 12: return "C";   
case 13: return "D";   
case 14: return "E";   
case 15: return "F";   
      } 
   } 
} 
function HexToNum(num1,num2) { 
numberS = document.forms[0].elements[num1].value; 
tens = MakeNum(numberS.substring(0,1)); 
if(tens == 'X') { 
document.forms[0].elements[num1].select(); 
document.forms[0].elements[num2].value=''; 
return false; 
} 
ones = 0; 
if(numberS.length > 1) // means two characters entered 
ones=MakeNum(numberS.substring(1,2)); 
if(ones == 'X') { 
document.forms[0].elements[num1].select(); 
document.forms[0].elements[num2].value=''; 
return false; 
} 
document.forms[0].elements[num2].value = (tens * 16) + (ones * 1); 
document.forms[0].elements[num1].value = document.forms[0].elements[num1].value.toUpperCase(); 
ChangeBackground(3, 4, 5); 
return true; 
} 
function MakeNum(str) { 
if((str >= 0) && (str <= 9)) 
return str; 
switch(str.toUpperCase()) { 
case "A": return 10; 
case "B": return 11; 
case "C": return 12; 
case "D": return 13; 
case "E": return 14; 
case "F": return 15; 
default:  alert('You must choose a number between 0 and 9 or a letter between A and F!'); 
return 'X'; 
   } 
} 
function ChangeBackground(num1, num2, num3) { 
document.bgColor = '#'+document.forms[0].elements[num1].value + document.forms[0].elements[num2].value + document.forms[0].elements[num3].value; 
} 
//  End --> 
</script> 
 
</HEAD> 
 
<!-- STEP TWO: Copy this code into the BODY of your HTML document  --> 
 
<BODY> 
 
<form> 
<table border=1 align=center cellpadding=10 bgcolor=white> 
<tr> 
<th>Color/Code</th> 
<th>Red</th> 
<th>Green</th> 
<th>Blue</th> 
</tr> 
<tr> 
<th>0-255</th> 
<td><input type=text name=rr_num size=4 maxlength=3 onKeyUp="return NumToHex(0,3);"></td> 
<td><input type=text name=gg_num size=4 maxlength=3 onKeyUp="return NumToHex(1,4);"></td> 
<td><input type=text name=bb_num size=4 maxlength=3 onKeyUp="return NumToHex(2,5);"></td> 
</tr> 
<tr> 
<th>HEX</th> 
<td><input type=text name=rr_hex size=4 maxlength=2 onKeyUp="return HexToNum(3,0);"></td> 
<td><input type=text name=gg_hex size=4 maxlength=2 onKeyUp="return HexToNum(4,1);"></td> 
<td><input type=text name=bb_hex size=4 maxlength=2 onKeyUp="return HexToNum(5,2);"></td> 
</tr> 
</table> 
</form> 
 
<p><center> 
<font face="arial, helvetica" size"-2">Free JavaScripts provided<br> 
by <a href="http://javascriptsource.com">The JavaScript Source</a></font> 
</center><p> 
 
<!-- Script Size:  3.91 KB -->
  
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