I used Dylon dye, but that was pretty much due to easy availability as it’s everywhere.
You do want to keep rinsing until it runs clear as if you don’t then what is left will be coming off onto you later - and especially as you have dyed seat covers
Follow the pre and post dye instructions for your particular dye. Most of what we did wasn’t dyed in the washing machine, but in buckets & bowls as it was just summer fun in the garden for friends kids.
No matter how much we would try to keep clean children would typically be going home with some
degree of coloured forearms as you can give them gloves and tell them to scrub with a brush afterwards but the best fun is messy
A wash in the washing machine would be done to finish off, but ideally we had it running clear by hand first
(the type of dye will effect that as some are cold/hand dyes and others are designed for use in washing machines - the most vibrant colours will probably be aimed at machine wash)
For future experiments don’t be restricted to dye, you can also “tie bleach”, either for the reverse effect on dark fabrics or to come up with more effects on top of dyed effects.
I would often have a big bucket of mixed dyes as a result, which could be used to see what it came
up with after a few days of dyeing, but it was more aimed at not having every child try to pour away used dye down the drain resulting in spillage over the path. That didn’t stop spillage as a neighborhood cat had an accident once, and didn’t return to being a white cat for a while
Checkout YouTube for different tie styles for different patterns and different tie techniques - most of ours was the fabric tied in knots, but you can get effects
with rubber bands or jute string etc
For multi colour effects you can add or takeaway knots as you add colours in a matching pattern, or you can totally untie after one colour and retie in a different manner for the next colour