The Minix3 console supports only 8 colors. If your terminfo database is reasonably recent, the recommended setting for TERM for the Minix3 console is minix.
Setting TERM to other values will not change the number of colors available to you. You can run other terminal emulators, if you are able to run X in your environment. Some of those support 256 colors.
The xterm program can be built for Minux3 (I did that last year, for Minux 3.2, finding some problems with its antiquated shell which were fixed since then). There is a port for xterm in pkgsrc (your question indicates that you are using pkgsrc).
Further reading:
- Installing Binary Packages (MINIX 3)
- Installing Source Packages (MINIX 3)
If someone has made a binary package for Minix3, it is available (prebuilt) with pkgin. Otherwise, you can use pkgsrc, which provides far more packages. Most (since Minix3 uses most of the "userland" from NetBSD) will build without problems.
Note however, that although the source-package page for Minix3 says
pkgsrc is used to build third-party software. This page describes how to use pkgsrc.
Minix is not listed on that site's Supported platforms.