I use Liquitex Flow-Aid as a medium for washes and for diluting paints. As far as I know, I have not had any problems with it. But, at a trip to the local arts store, I noticed some thing odd. Either the formula has changed slightly, or my old (and how old I do not remember) bottle of Flow-Aid has aged, but there is a color difference between 'fresh' Flow-Aid and my venerable stock:
The new bottle is on the right.
So, I made a new batch of Flow-Aid (I dilute it to 5% for use). Will I be able to tell the difference? Probably not!