Docker does not trigger login or invoke /etc/profiles?

Question

Trying to deal with the problem of

dircolors: no SHELL environment variable, and no shell type option given

when I start my docker container.

So from What sets the $SHELL environment variable? it can be infered that login(1) is not triggered,

And I've put a env.sh in /etc/profile.d:

$ cat /etc/profile.d/env.sh 
SHELL=/bin/sh
$ ls -l /etc/profile.d/env.sh 
-rw-r--r-- 1 root root 14 Feb 24 18:21 /etc/profile.d/env.sh

and apparently that is not invoked either, as when I'm within my docker container, all that I have is:

$ env | grep SH
SHLVL=0

How to solve the SHELL environment variable definition problem?