Hexa colors in PHP loop

colors.php

<?php

define('PAD', 1);
define('WIDTH', 1);
define('HEIGHT', 1);

ob_start();

echo '<table cellspacing="0" cellpadding="0" border="0" style="margin: 0; padding: 0;">';

for ($cell = 0, $col = 1, $line = 1, $nbLines = (255/PAD), $nbCells = $nbLines * $nbLines; $cell < $nbCells; $cell+=PAD) {

    if ($cell % $nbLines == 0) {
        echo "\n",'<tr>';
        $col = 1;
        $line++;
    } else {
        $col++;
    }

    $red = str_pad(dechex($nbLines - $line), 2, '0', STR_PAD_LEFT);
    $green = str_pad(dechex($col), 2, '0', STR_PAD_LEFT);
    $blue = str_pad(dechex($line), 2, '0', STR_PAD_LEFT);
    $color = '#' . $red . $green . $blue;

    echo '<td style="width:'.WIDTH.'px;height:'.HEIGHT.'px;background-color:'.$color.';"></td>';

    if (($cell+1) % $nbLines == 0) {
        echo '</tr>';
    }

}

echo '</table>';

ob_end_flush();