Good question. Once you've picked your device and device color, you'll move on to trying out and selecting your strap - or straps, we won't judge if you want multiple!
The first step is to select your strap material. Once you've done that, the large color swatch icons will display the color options available for that particular material. The customizer will only load strap material and color options that will work for the device you've selected so no need to worry about whether they'll support the device you've picked.
Still a little confused? No problem! See the chart below for a full explanation of color availability.
Color Swatches Explained:
Large Color Swatch + Blue Outline
Color available in that material and currently displayed with your selected device
Large Color Swatch
Color available in that material
Large Color Swatch + Red Slash
Color available but currently out of stock
Small Color Swatch
Color available in different strap material only
Small Color Swatch + Red Slash
Color available in different strap material but currently out of stock