[Request]Enemy Name Color Change

#include <iostream>
#include <string>
#include <vector>
 
using namespace std;
 
int convertFromHex(string hex)
{
    int value = 0;
    
    int a = 0;
    int b = hex.length() - 1;
    for (; b >= 0; a++, b--)
    {
        if (hex[b] >= '0' && hex[b] <= '9')
        {
            value += (hex[b] - '0') * (1 << (a * 4));
        }
        else
        {
            switch (hex[b])
            {
                case 'A':
                case 'a':
                    value += 10 * (1 << (a * 4));
                    break;
                    
                case 'B':
                case 'b':
                    value += 11 * (1 << (a * 4));
                    break;
                    
                case 'C':
                case 'c':
                    value += 12 * (1 << (a * 4));
                    break;
                    
                case 'D':
                case 'd':
                    value += 13 * (1 << (a * 4));
                    break;
                    
                case 'E':
                case 'e':
                    value += 14 * (1 << (a * 4));
                    break;
                    
                case 'F':
                case 'f':
                    value += 15 * (1 << (a * 4));
                    break;
                    
                default:
                    cout << "Error, invalid charactare '" << hex[a] << "' in hex number" << endl;
                    break;
            }
        }
    }
    
    return value;
}
 
void hextodec(string hex, vector<unsigned char>& rgb)
{
    // since there is no prefix attached to hex, use this code
    string redString = hex.substr(0, 2);
    string greenString = hex.substr(2, 2);
    string blueString = hex.substr(4, 2);
    
/*
    if the prefix # was attached to hex, use the following code
    string redString = hex.substr(1, 2);
    string greenString = hex.substr(3, 2);
    string blueString = hex.substr(5, 2);
*/
    
/*
    if the prefix 0x was attached to hex, use the following code
    string redString = hex.substr(2, 2);
    string greenString = hex.substr(4, 2);
    string blueString = hex.substr(6, 2);
*/
    
    unsigned char red = (unsigned char)(convertFromHex(redString));
    unsigned char green = (unsigned char)(convertFromHex(greenString));
    unsigned char blue = (unsigned char)(convertFromHex(blueString));
    
    rgb[0] = red;
    rgb[1] = green;
    rgb[2] = blue;
}
 
int main()
{
    string hexColor;
    vector<unsigned char> rgbColor(3);
    
    cout << "Enter Hex value (must be 6 valid Hex digits): 0x";
    cin >> hexColor;
    
    hextodec(hexColor, rgbColor);
    
    cout << "\nWhen 0x" << hexColor << " is converted to RGB, it becomes:" << endl;
    cout << "R: " << int(rgbColor[0]) << endl;
    cout << "G: " << int(rgbColor[1]) << endl;
    cout << "B: " << int(rgbColor[2]) << endl;
    
    system("pause");
}