Does dosbox differ from a real tandy in this respect?
Sort of; DOSBox does not have an option to emulate composite video artifacts with machine set to Tandy or PCjr mode, only in CGA mode and then only with the 640x200 resolution and color burst bit set. It does however correctly emulate what a Tandy 1000 with an RGB display would show.
The /c2 will display correctly in color on a real Tandy with a composite monitor. It will display with incorrect colors on a CGA with composite monitor. It will display as black and white on any system with an RGB monitor. Likewise, the /c1 will display with the incorrect colors on a Tandy but with correct colors on CGA with composite displays, and black and white on any system with RGB display.
For some reason, the hue in the 640x200 mode on Tandy 1000's (all the ones I've tried at least) is different than with a true CGA card. This game takes that into account. Kinda surprising really, I'm not sure how many Tandy 1000 owners actually used a composite display, especially in 1989; 16 colors on an RGB display was one of Tandy's selling points!
Here is what the /c2 mode looks like on a real Tandy 1000: