Gusty and Moondancer look to have old ink stains - they tend to 'bloom' like that after being on there for many a year. Sunfading would be the go-to solution for them.
Parasol looks more like possibly metallic paint, particularly on the hind hoof. Try acetone / nail polish remover, but keep it /away/ from any paint or glitter areas - it'll take them right off. Also use in a well ventilated area, preferably outside. Anything that's left will also have to go the sunfading route.