Some of your 'shortcuts' are not good ideas. Definitely start with cold water. Definitely bring up the temp slowly. Definitely do not boil. Do add aromatics upfront to the broth, but remove them as they get mushy so they don't cloud it.
Standard ratio for beef broth would be: 8 pounds of bones to 6 quarts of water to 1 pound of veggies (onion, leek, carrot) to one 'boquet garni', essentially garlic, rosemary, anise flavoring for pho, and bay leaf, plus whatever else I forgot.
If you have 'pond water', which I interpret as thin-tasting, you probably put too much water in the second time -- this is fixable by slowly evaporating out the water until it gets to a good texture. If you skimmed properly, it will be clear as you do this. I will typically strain through a kitchen towel or cheesecloth as the liquid evaporates down.
I'm guessing you put in like a gallon of water, so you had like three or four times too much water.
As a warning which you probably already know, you are not going to be able to duplicate your local pho joint's broth -- the broth recipe is the thing for pho makers, and they probably have a bunch of tricks they use, including using a neverending supply of yesterdays pho, that you won't be able to do at home. That said, you should be able to get a good beef broth if you follow some basic rules for making stock.
Let it rest anyway. Even at low temperatures, the juices will be flowing through the meat. Resting stops this process.
As for the strange colour-changing meat, I suspect you just weren't observant. Meat that has gone brown will not spontaneously go pink again.
Best Answer
It's probably less to do with the amount of juices that came out of the rib roast and more to do with the extended caramelisation of those juices produced by overcooking. Those burnt, caramelised bits left in the bottom of the pan are full of flavour and it's probably that, that added so much more flavour to your gravy than you're used to.
Just replicate it the next time you make a rib roast. Once the roast is done, take it out, cut a slice or two of the meat off, chop it up into small pieces, put it back in the pan and continue cooking until the pieces are burnt and caramelised. Make your gravy as before.