Purchase 2 ounce makeup bottles from Walmart for as many colors as you think you will need. Next, fill them with water. Then add 30 drops of re-inker, shake it to mix and spray many backgrounds for your stash. Have fun playing and experiment with various color combinations.
In addition, make a spray paint “booth” out of a cardboard box (abt. 15 x 15 inches) by cutting off the flaps and lining the very back (bottom of box) with wax paper so there isn't any accidental spray leakage from there to your work surface.
I recently saw a bottle of similar solution at a scrapbook store for $13.00.
Postscript: You can also use a few drops of acrylic paint to water, however, be sure to rinse the nozzle with water after using it as the paint may clog it up.