You can do it like this
$(function(){_x000D_
$("tr").find("td:eq(0)").css("color","red");_x000D_
})
_x000D_
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>_x000D_
<table>_x000D_
<tr>_x000D_
<td>col_1</td>_x000D_
<td>col_2</td>_x000D_
</tr>_x000D_
<tr>_x000D_
<td>col_1</td>_x000D_
<td>col_2</td>_x000D_
</tr>_x000D_
<tr>_x000D_
<td>col_1</td>_x000D_
<td>col_2</td>_x000D_
</tr>_x000D_
<tr>_x000D_
<td>col_1</td>_x000D_
<td>col_2</td>_x000D_
</tr>_x000D_
</table>
_x000D_