I make use of emulation regularly. While I do still have my original Radio Shack Color Computers from the 1980s, it is usually more convenient to just load up an emulator. For short experiments in BASIC, or casual game playing, this works just fine. However, emulation is not perfect and sometimes you run in to something that stands out.
These purple colors were generated on the XRoar 1.0 emulator when emulating a later-model Color Computer 2 with an updated T1 version of the 6874 VGD video chip.
I had never seen such colors, but since I had never had a T1 CoCo I assumed it was just another odd secret that chip held I was just unfamiliar with.
The first sign that this might be an emulation issue was that the purple only showed up when the emulator was using simulated RF output. In that mode, it tries to replicate the fuzzy appearance of TV output. turn that simulation off and the screen changed to expected orangish reddish alternate color.
While I do not know the details on what caused this, XRoar has been updated to no longer produce these purple colors in this mode.
You can pick up the latest XRoar emulator (that adds support for the Color Computer 3 and MC-10) here: