Answered my own question. For anyone else looking to do it (change the cell colour of the welcome header), simply follow these steps.
1. Open Style Manager -> All Style Options -> Additional CSS Definitions
add to the bottom:
Code:
.welcomeheader
{
background-color: #FFFFCC;
color: #000000;
}
Replace #FFFFCC with whatever color code you want the cell to be.
2. Open your welcome_headers template. Find <td class="alt1">. Change to <td class="welcomeheader">