Hi Leann, here's a link to some info. Are your cushion covers removable. If not, you may want to paint them rather than dye them.
Here's info on painting them.
Use fabric paint.
What are they made from? If they were meant to be patio cushions, they should be a synthetic fiber. Cotton breaks down too easily outside.
Synthetic fibers only accept dyes made for them. Rit makes them and they’re easy to find.
To make the dye take better, bring it to a boil in a stainless steel pan and take the pan outside where your cushions are sitting on plastic tarps. With a big paintbrush, paint the hot dye on the cushions. Maybe a small paint roller.
I don’t think I would want to handle hot dye and try to pour it into a plastic spray bottle with plastic funnels, that just sounds like an accident waiting to happen, to me.
Blot off the excess dye when your finished with all of them. Working while the dye is hot, Is essential.
I would try using a fabric paint on an inconspicuous spot to see how your cushions take the paint, If it does, then use this paint to paint the entire cushion.
Have you thought of painting? https://www.hometalk.com/36994925/patio-cushion-rehab-with-paint