Well, I retested the 2C-I with Marquis and it went yellow to brown quickly, then the brown changed to blue/black over the course of a couple minutes.
I'm not sure what is going on here. I just now tested three different batches of 2C-I (two of which are 100% verified/aunthentic) and other than slight variences in shading, probably due to different amounts used (I just eyeballed a tiny, tiny amount straight out of each vial.) All tests produced a light green reaction with marquis, as expected.
If the concentration of 2C-I is high enough, I could see how it could result in a blackish color, but I have no idea how you are getting a yellow/brown/blue/black reaction. And just to double check that I am not loosing my mind, I confired with a chem friend and he indeed confirms that 2C-I should/does indeed produce a green color with marquis, similar to 2C-B. Erowid, and a few other places I have checked also report a green reaction with marquis and 2C-I.
Could your marquis be old? Well, actually the stuff I just used is now a bit old, so I really don't know why you are reporting the reaction you are. Very interesting mystery.
As far as the reliability of that erowid page, I've tested 2C-B, 2C-C, 2C-D, 2C-E, 2C-T-2, 2C-T-7, MDMA, MDA, methylone, DOB, TMA-2, DPT, and maybe a few others with marquis. I recall everything checking out but its been many years since I did that. I have not personally worked with the other regents to any significant extent, so I can not comment on those either.
Morningglory seed, what is your opinion on combining 2-CI or 2-CC with MDMA?
I have had one experience with 2C-I and MDMA. We took 120mg of MDMA, and a few hours later ate 15mg of 2C-I. Neither of us felt this was a good combination. There was just way too much energy/stimulation and my mind raced like crazy. Neither of us would repeat.
I also have had one experience with MDMA and 2C-C. I think I took 30mg of 2C-C, and ate 80mg of MDMA a few hours into it. This was a nice combination, but nothing special.
2C-B and MDMA on the other hand is absolutely fantastic, and I consider 2C-B on its own to be a mediocre psychedelic at best.