Table Column Colors

I have two columns, I am trying to make the first column #f8f8f8f and the second column #ffffff. The second column is working, the first column is not.

This is the css I am using:
/* first column */
.main_color tr td:nth-child(1) {
background-color: #f8f8f8;
text-align: left;
}

/* first column */
.main_color tr td:nth-child(2) {
background-color: #ffffff;
text-align: left;
}

Any ideas of what would get the first column to work?

Thank you.