Other than navy blue, I've never tried any blues, and that time I was doing it to cover up a mishap and as such they ended up otaku. I also did a forest green batch the same way, those are visible with enough light. The one time I tried black on the darker keys (the "pebble" originally ones) that came out as more of a dark brown than black - apparently there were variations even at the time of black formula. This Model M has green keys that are great looking, but I'm not even sure which green it was anymore as I did it some time ago.
Yes, now that I'm paying attention I am as certain as I can be. With the exception of the one mishap (which was two sets of keys at once with a mix of liquid dyes), every time I've done it has worked perfectly fine. Right up until the last time I tried to do it and I got a new something (some kind of blue I suspect) which didn't work and then now even new yellow won't work.
I'm also not sure it matters what steps are used to do it, I've done with salt, without salt (supposedly salt is to make it set on fabrics) and I usually do one packet per set of keys with completely different amounts of water. When I'm dumping out the water there's also always enough color left there that I suspect I could do more than one set of keys at once - or even in series - with the same packet. When I did it today I even did what someone else said he did, which was to bring the dye in some water to a boil in the microwave, and have the keys already simmering in water and then just dump it all in. Almost immediately the red started taking.
If it's been inconsistent, keep in mind that 2011 was some time ago and also how long these dyes can sit on the shelves. The 2010 marked one I got yesterday was an orange, and clearly had to have been sitting there for some time. To add even more variation to the mix is the fact that when they were changing formulas in 2011, they did it gradually for the powders. So even some colors at that time will work, if the batch was early enough, but I'm not willing to experiment when I know a hard and fast cutoff date to look for. There was a disc golf forum I ran across which had people trying to work out which batches would work.
For the record, on RIT's own site they have a blog post about the formula change, and the fact that the new formula doesn't work on certain plastics anymore. Even if it's not mentioned specifically PBT is obviously one of them.
Yes, I can take some pictures.