problem using su

I lose the convenience of having executables and directories listed in color when I su to root. I log in as "tom" then do su. As tom I get color listings, but when I su, it's back to b/w. I've read the /etc/profile file and DIR_COLORS file, but don't know how to activate them when I do su. And why should aliases defined to user tom disappear when su'ing to root? User root doesn't have this problem. The color listings work fine. This is a SuSE 7.2 pro box where it's just me learning some C++ and Qt (and Linux). I basically don't have a firm concept of what all kicks in and in what order during Linux boot. And to make matters worse this varies by distro it seems.