MySQL to Excel -- Setting Header Row Width and Color in Excel?

How to use php setting my excel header row's width and color?

Very few information for a question ... anyways, I recommend to use PHPExcel:
http://phpexcel.codeplex.com/

It depends on how you export the file. If you use a class that exports to real .xls you will need to use its methods.

If you export to a HTML table you can use a colgroup

<table>
    <!-- Column 1 -->
    <colgroup width="xxx" style="background-color: somecolor;">
    <!-- Column 2 -->
    <colgroup width="xxx" style="background-color: somecolor;">
    <tr><td></td><td></td></tr>
</table>