Colour Modes and Spaces – 3

The Mode Palette is under the Image file menu in Photoshop.
In this screen grab you can see that the mode is RGB and we are working with 8 bits per channel – i.e. levels 0 to 255 where 0 is no colour and 255 is maximum colour. So 255 in the red channel means maximum red saturation for the colour space – see this short explanation of how computers define colour

These two settings – RGB Color and 8 Bits Channel are the ones you need to select. Don’t worry about the others for the time being, just check to make sure these options are ticked.
Just to tickle your appetite, maximum saturation varies depending upon the “flavour” of RGB. Red255 will be more saturated in adobeRGB (a wider colour space) than it is in sRGB – that’s why the colour profile attached to the image file is so important – we’ll deal with that later ! )