correct

<?php
    for ($i = 51; $i <= 255; $i+=51) {
       echo "<tr>\n";
        $colorRed = "rgb($i, 0, 0)";
        $colorGreen = "rgb(0, $i, 0)";
        $colorBlue= "rgb(0, 0, $i)";
        echo "\t<td style = 'background-color:$colorRed'></td>";
        echo "\t<td style = 'background-color:$colorGreen'></td>";
        echo "\t<td style = 'background-color:$colorBlue'></td>";
        echo "</tr>\n";
    }
    ?>