Purple!!
Sounds like you've got both Qi and |Blood stagnation in your knuckle. You burst some vesicles with the punched aand caused stagnation there too. Untill it gets cleared it will remain and if you do further injury to it might get worse, with the possibility of causing more long term damage to your fingers and general hand kinesthetic in general.
See a good Herbalist or Acupunturist.
Did you apply any Dit Da Dow on it afterwards?
" Don't confuse yourself with someone who has something to say " - The Fall
" I do not like your tone/ It has ephemeral whingeing aspects " - The Fall
" There are twelve people in the world/ The rest are paste " - Mark E Smith