Here are the various problems with all of the above suggestions with Future that I discovered...
1) When using food coloring, you end having to mix more then you need. If you're using an Empty .5oz bottle filled with Future, a single drop of food coloring (as dispensed from the food coloring bottle) contains too much water and dillutes the Future increasing the time it takes to dry by a fact of about 10x... also because the drop is so large making subtle tints is rather difficult.
2) When using Food Coloring powders, they never seem to disolve completely in the Future and you end up with little grains when you paint or dip it. Not to mention using them will clog your airbrush unless you're using a siphon brush, but you'll end up with a good tint with little grainy spots everywhere.
3) Tamiya Translucents are great I agree but harder to find. My local hobby shop doesn't carry any so I'm forced to purchase from online. However you run into the problem there of hoping that the color that you purchased is the right one, and have to wait for itto arrive and when it finally does come, it's not the right color and now you're outnot only the price of the paint plus the shipping but the time you wasted waiting for them to get to you only to find it doesn't work for the project you're working on.
4) Future has become a generic term for Clear Acrylic Floor Wax like Fridge is a generic term for Fridgiair. You can usually find an acceptable substitute in just about any grocery store. It usually comes in a container with a squirt top and is crystal clear.
5) Yes you can thin down Future with water, works well for Airbrushing because using it straight from the bottle in an airbrush is a bit thick... however when you do mix it with any water based substance you will increase the drying time. However I have heard of mixing it with Rubbing Alcohol and that isn't an issue, but I have never done so to confirm that claim.
6) Mixing with Acrylic paint didn't really work well. It was difficult to create an even mix that would create a true "tint" in the color you want. And alot of the paints also use some powders and again you get that "grit" in your tint.
In my experience, the printer ink works best for tinting due to it's extremely small concentrated nature. It mixes very well and evenly with Future and you can create small batches for your use. I've got 4 empty Testors paint bottles that I filled with Future and added each color to. I have yet to use up all of any of the colors I've made and they have been a staple in my paint kit forever! Its a much cheaper solution to purchasing Tamiya or Vallejo transparent paints (seeing as each bottle of those goes anywhere from $3.00 to $8.00 a .5oz bottle). A 24oz bottle of Future cost me $1.98, and a printer ink refill kit was like $10 and was used to refill my printer cartridges so was readily available. So for $12 I have a tool in my toolbox that has been there for at least 20 years. Instead of only 2 or 3 little bottles that may work for my projects.
I still have 3/4 a bottle of Future because what's really nice about it, is this. When you use it for dipping, you fill a small container with it, dip your parts and then pour it back in the bottle. Its wonderful stuff for modelers and I can't recommend it enough.