Considering the game you found this option in and the name itself, my guess is the "Explorer" was a special computer system aimed at children and probably uses a standard EGA or MCGA graphics system. In fact, searching the net for such a computer pulls up a more modern system that is indeed intended for kids.

Have you tried testing to see what modes this setting works under (if any) in DOSBox?

It's all I get when using Tandy mode, ega, vgaonly and cga,

This site says that "CGA (Tweaked) mode is 'Explorer with RGB Monitor - 16 colors'" for KQ1, at least.

...it almost seems as though this "Explorer" thing is actually a 640x200 resolution that should be running 16 colours but is instead triggering a CGA 320x200 4 colour mode.

EDIT: Nevermind. I did some more investigating of the pixels and it's definitely a 320x200 mode running 16 colours. :P

Young Explorer computer is released in 1998.

http://www-03.ibm.com/press/us/en/pressrelease/2695.wss

Why IBM would released a 16 colour computer when VGA could be used?

Well, it can't be that one specifically because it came 8 years after this game. :P

the "HeadStart Explorer" was a PC/XT clone introduced in 1989:

http://www.obsoletecomputermuseum.org/explode/
http://good-times.webshots.com/photo/28319527 … 074179466dMvYFt
http://www.usedprice.com/items/computer/head- … rer-247869.html

From what I could find online, it had on-board CGA compatible graphics. Possibly with some enhancements - that Webshots link looks like a high resolution colorful GUI.... so 16-color support seems logical.