integer Ord(string chr)
{
    if (chr == "")
        return 0;
    chr = llGetSubString(chr, 0, 0);
    string hex = llEscapeURL(chr);
    if (llGetSubString(hex, 0, 0) != "%")
    {
        // Regular character - we can't take advantage of llEscapeURL in this case,
        // so we use llStringToBase64/llBase64ToInteger instead.
        return llBase64ToInteger("AAAA" + llStringToBase64(chr));
    }
    integer b = (integer)("0x" + llGetSubString(hex, 1, 2));
    if (b < 194 || b > 244)
        return b;
    if (b < 224)
        return ((b & 0x1F) << 6) | (integer)("0x" + llGetSubString(hex, 4, 5)) & 0x3F;
    integer cp;
    if (b < 240)
    {
        cp = (b & 0x0F) << 12;
        cp += ((integer)("0x" + llGetSubString(hex, 4, 5)) & 0x3F) << 6;
        cp += (integer)("0x" + llGetSubString(hex, 7, 8)) & 0x3F;
        return cp;
    }
    cp = (b & 0x07) << 18;
    cp += ((integer)("0x" + llGetSubString(hex, 4, 5)) & 0x3F) << 12;
    cp += ((integer)("0x" + llGetSubString(hex, 7, 8)) & 0x3F) << 6;
    cp += (integer)("0x" + llGetSubString(hex, 10, 11)) & 0x3F;
    return cp;
}

integer iValidRange1Start = 48;
integer iValidRange1End = 57;
integer iValidRange2Start = 97;
integer iValidRange2End = 102;
integer iValidLength = 6;
integer isValidColorstring(string sInput)
{ //Returns true if sInput is a valid color-string.
    integer iCounter;
    integer iOrd;
    if (sInput != llToLower(sInput))
    { //Only lowercase-characters are allowed.
        return FALSE;
    }
    if (llStringLength(sInput) != iValidLength)
    { //Invalid length.
        return FALSE;
    }
    for (iCounter = 0; iCounter < iValidLength; iCounter++)
    {
        iOrd = Ord(llGetSubString(sInput, iCounter, iCounter));
        if ((iOrd < iValidRange1Start || iOrd > iValidRange1End) && (iOrd < iValidRange2Start || iOrd > iValidRange2End))
        {
            return FALSE;
        }
    }
    return TRUE;
}

integer iComponentLength = 2;
string sHexPrefix = "0x";
float fColorMax = 255.0;
vector vColorFromHex(string sColor)
{ //Convert hex-string (e.g. "aaff00") to vector color.
        string sX; string sY; string sZ; integer iHelper; vector vColor;
        iHelper = 0;
        sX = llGetSubString(sColor, iHelper, iHelper + iComponentLength - 1);
        iHelper = iHelper + iComponentLength;
        sY = llGetSubString(sColor, iHelper, iHelper + iComponentLength - 1);
        iHelper = iHelper + iComponentLength;
        sZ = llGetSubString(sColor, iHelper, iHelper + iComponentLength - 1);
        
        vColor = <((integer)(sHexPrefix + sX)) / fColorMax, ((integer)(sHexPrefix + sY)) / fColorMax, ((integer)(sHexPrefix + sZ)) / fColorMax>;
        return vColor;
}

integer iListener;
integer iChannel = -938475;
float fTimer = 30.0; //Seconds.
string sMessageTextbox = "Please enter the hex-code to re-color this prim-face, e.g. aaff00";
string sMessageWrongColor = "Invalid color-code.";
integer iTOUCHFACE;
integer iTOUCHPRIM;
default
{
    touch_start(integer num_detected)
    {
        if (llDetectedKey(0) != llGetOwner())
        { //Only listen to owner.
            return;
        }
        iTOUCHFACE = llDetectedTouchFace(0); //Store face and prim.
        iTOUCHPRIM = llDetectedLinkNumber(0);
        iListener = llListen(iChannel, "", llDetectedKey(0), "");
        llSetTimerEvent(fTimer);
        llTextBox(llDetectedKey(0), sMessageTextbox, iChannel);
    }
    listen(integer channel, string name, key id, string message)
    {
        llSetTimerEvent(0);
        llListenRemove(iListener);
        //Delete timer and listener.
        if (isValidColorstring(message))
        {
            llSetLinkColor(iTOUCHPRIM, vColorFromHex(message), iTOUCHFACE);
        }
        else
        { //Invalid color-code.
            llOwnerSay(sMessageWrongColor);
        }
    }
    timer()
    {
        llSetTimerEvent(0);
        llListenRemove(iListener);
        //Delete timer and listener.
    }
}