Dyeing acrylic

[hydrolagus.livejournal.com]

I am doing a Hogwarts uniform for Halloween and have not had much luck finding a dark grey v-neck sweater that I can afford, so I've been trying to dye a light grey one darker. So far, I've tub-dyed it with Jaquard and washing-machine-dyed it with Rit and it's still lighter than I'd like. If I hit it again with the Rit, is it likely to get any darker? I'll show it off once I'm done modding it.