Hello,
You can one of a few things:
First thing you need to do is make sure there are no IPs owned by the Reseller. There probably is, so you have to clear any association with the Reseller and the IP.
Admin Panel -> IP Manager -> Find any IP's that are assigned to Reseller "colin" -> select those IP's and click "Remove from Reseller". If there are any users on that IP, you'll have to manually edit /usr/local/directadmin/data/ips/1.2.3.4 and set "value=0", then you'll be able to remove the Reseller from the IP.
By doing this, the /etc/httpd/conf/ips.conf file will be rewritten with the correct setup, thus not giving you the error.
Other solutions include "useradd colin" or just manual configuration of the /etc/httpd/conf/ips.conf to change user "colin" to "apache" while you fix the error at it's source.
John