That's amazing Jane. I used to dye shoes too in the 60's never thought about gloss paint so, something else I will experiment with. Thanks.
As has been mentioned finding dyes now is not as easy as it was back then when there were certain dry cleaners who would dye curtains professionally. I buy dyes at a couple of local ironmongers, failing that I buy them on Amazon.
Yes, I remember tie-dyeing Aka 
I dye most things in the washing machine and the instructions are, after dyeing, run a normal wash in an empty machine. This cleans out any remaining dye successfully.
I found out too mcem, anything with elastic in it won't work. Best results with 100% cotton.
I use Colour Catcher sheets that I buy in the pound shop if I'm not too sure about something that might run in a mixed wash.