Technically, chinese mustard powder is slightly different to Colman's; it's all down to the blend of different types of seeds. Colman's combines brown & white, whereas I think the authentic chinese powders only use brown (which is more pungent). But there's very little in it, and Colman's is still very pungent when mixed fresh, so it is a perfectly good substitute. Personally, I have been mixing hot water with it to make "chinese" mustard, as it tastes more like what I would describe as chinese mustard. But I don't know exactly what it is you've tasted, so it's hard to compare. Colman's mixed with cold water, to me, is "english" mustard (well, that's what we've always had, and what my Grandpa had with his boiled egg & ham in the morning!), so the hot water version tastes sufficiently different to distinguish it from the "english". It doesn't seem to make a huge difference to the heat level, though, they're both pretty pungent! I've come across recipes for chinese mustard which use cold, warm, hot & boiling water, so I'm not sure which is really the "correct" version. Vinegar is sometimes added to preserve the flavour for longer, but if you're eating it stright away I don't think it is strictly necessary. Some people add a little oil & salt. The pre-prepared versions often come with all sorts of things added: turmeric (mostly for colour), sugar, vinegar, garlic, spices etc, although I once read the ingredients on an S&B one & it was just mustard & turmeric. It's hard to say what goes into a "chinese" mustard, as I'm pretty sure there isn't just one "official" version, and the types you have tasted may be different to the ones I've tasted. But I'd hazzard a guess that, much like the "english mustard" I grew up with, the simpler recipe (i.e. plain mustard flour with water) is closer to a "real" homemade chinese mustard.