Since someone is offering to sell them (how dare them!) I am offering a free inkjet formula for dummies. Here it is:
Get a food coloring. (red, blue, green, black). Get glycerine. Mix about 2-5%. You are done. It's not perfect. Use only dyes to prevent clogging.
For the more elaborate setups you need to get PH to alkaline 8-11 -this is done to prevent clogging and control colloidal suspension. Mix right ratios of organic polar/nonpolar solvents. (polar/non polar controls the droplet size and penetration when printed. For you fancy people, you need some surfactants (detergents) to reduce surface tension (get droplets size small) find some antifoam to reduce bubbles in the tiny nozzles. Pay attention to those non polar sovents such that it must be sticking to the container and not the color. If the color sticks to the container, you will have a very messy inkjet nozzles. I cannot state exact formula for more fancy ones since chemical suppliers sell in Bulk and cannot afford it. So you have to find them yourself.
Since I am too poor to afford even a refill, I make my own (since I am an unemployed R&D chemist). In the meantime, the dummy formula is O.K. just try to use it once every day to prevent clogging.