Hi, it could be blood. Also, do you have any other symptoms such as itching, burning, discharge, Pain? You could have bacterial vaginitis. This can be caused by a new sex partner, just due to the change or it can be an infection. But it is often caused by a change in the pH of the vagina due to bacteria that normally there and if you use a douche or something changes the normal bacteria and you get an overgrowth of the wrong bacteria or a yeast it can cause problems . It can be tested for . If it is not blood then you should see your doctor to have a few tests.
mkh9
If by 'done stuff' you mean (penetrative) sex when you were a virgin before, it might be just some residual bleeding. By penetrative sex, I mean, penis going into vagina. I don't think that just fingering could cause bleeding even if you were a virgin.
Did you two use condoms or are you on the pill? If not, how recently was your last period?