With the pre-AGI version of King's Quest, all you need to do is set machine=svga_s3 (rather than machine=cga) and boot the image. With the AGI version, you can force the selection of the CGA driver by also setting machine=svga_s3 and then starting the game using "sierra -c". (Note that this uses that palette but will look slightly different than those screenshots simply because Sierra changed the graphics ever so slightly for being able to support EGA. This is quite noticeable in the first screen where the outlines of the bricks and the shadow inside the tree are lighter).

The -c tag is for the CGA composite mode, which was meant to be used with a TV set. The -r tag uses the CGA RGB mode. In DOSBox, the -c tag requires the cga machine to display properly. Playing King's Quest with the cga machine, without any tags, uses the composite mode.

Also, I'm pretty sure that all versions of King's Quest (except the 1990 SCI remake), even the non-EGA versions, used a version of the AGI engine.

Thankyou Kippesoep and Tsyu, it's working perfectly now!

In game, you can switch between RGB and composite mode using Ctrl-R. What he asked for was to have the regular CGA palette, rather than the RGB palette. The only way to get that is to disable CGA emulation and overriding EGA detection. Hence the -c.

And yes, it was AGI (which was invented specifically for KQ). The terminology on that page calls it pre-AGI, which is the booter version.