You can actually tell by looking at the tab for your document. It will tell you. ex. rgb/8, cmyk/8, index/8, etc. First part is the mode the number 8, 16 or 32 is the bits per channel. These are changed in the image menu Image>Mode>RGB for example. You don't necessarily have to change it your self, for the mode to change, just opening an image that is saved with that mode is enough.
Besides, in greyscale or bitmap, you would not see any colors for the color swatches, just black and white and shades of grey.
If you are uncertain about anything, feel free to capture your screen and post it on the forum with the layers panel open. This can tell us quite a bit of information.