color picker not working

I am using the color picker  to pick a color to paint with. I am trying to choose green, but the picker only selects black or white. this happens with other colors as well,, such as red, blue etc. I  go to the foreground color box, click on it and that takes me to the color picker. I choose my desired color, move the little circle to the desired shade and hit OK. the foreground color turns either black, white or grey. when i draw a line, the color is what photoshop made it; ie; either black, white or grey. I have been trying to fix this for awhile now with not solution. what am i doing wrong? thank you