i'm sorry, but i think i realized the problem, can you have two %s's for just one string?
try the following:
printf("<td bgcolor=$row_color><font face=verdana size=1><b><a href=mailto:%s>%s</a></b></font></td>",$myrow["email"], $myrow["email"]);
if that doesn't work, try defining the variables before the printf function and just using them as you use $row_color.
-matt