Photoshop Colour Palettes

Hi,
I wonder if anyone can answer a Photoshop question please.
I want to create a pallete with only six colours of my choosing on it. Ideally I'd like to pick the colours using the eyedropper tool from the image and then create a limited palette which I will use to work on the image. The pallete would then have, for instance, Black, Dark grey, Grey Green, Olive green, pale green and white.
Is this possible? Does Photoshop allow this?
Thanks,
Bruce.

Okay. I've found now the answer to this (plus lots of other free Photoshop advice) at a site called photoshopessentials. It showed me how to clear the colour swatch and replace the colours with colours that I choose with the eyedropper tool.
B.