I have one item with multiple colors I want to show on my front page's collection. I created a new collection and added a new "Featured Collection" in my customized theme page, but it's only show one thumbnail. I want it to show at least 5 thumbnails.
To display your colour variants as seperate product cards will either require editing thing theme files and adding some logic to do that, or move the colour variants to individual products instead of variants of one product - this is the reason why a lot of merchants use seperate products for different colours.
The code would basically involve adding some additional logic into your featured collection section, and inside the product loop that generates the cards, add an additional loop to loop through all of the product variants, check for the option name of 'colour', and render an extra card for that variant.