I just got a new Bamboo Tablet Pen and its not working! I need help quick!?

Okay, to start off, my grandma just bought me a new Bamboo Tablet Pen, I'm one of those editing people. I Use GIMP. It works perfectly fine. But one problem. I set my colors and when I start to draw it changes to the original colors the : Black & White colors.. I wanted to use Pink & White (the little squares you see) & it changes back to the Black and white. It really makes me mad because I don't know how to fix it. & every time I use the "paintbrush" it just changes to the color black instead of pink and then when i keep writing or something its like a brush that fades away each time you write or draw. I don't know how to fix it. Please help I'm so desperate. :(