And done.
Refer to the excellent answer here: https://community.shopify.com/c/online-store-and-theme/show-all-product-variants-in-the-collections-...
The basic methodology is as follows: find main-collection-product-grid.liquid (or equivalent) in your theme code. Look for the loop that starts {%- for product in collection.products -%}
Within this loop, swap in the code referred to the the answer linked above, above and below the <li> that contains the snippet that renders a product. There'll be a bit that goes above and a bit that goes below. I had to tweak this a little for my theme, but it was basically a Dawn-ish theme so all good.
The important part of that code is that for products with multiple colour variants, you're adding in a further loop: {% for option in product.options %}
This is the key bit - it iterates over the variants of each product. You then filter that down to the colour option, get that as a variant object, and display a product card for each variant.
This is the second part of the tweak - you need to create a new snippet product-card-variant, which should be a copy of the existing product-card snippet, but with an extra argument: variant, which you specify in 'accepts' as product_card_variant.
Within your new product-card-variant snippet, find the bits that relate to the image you're going to display and change those to use product_card_variant as a data source instead of product_card_product.
Find the h3 tag that outputs the product name and use the append: filter to add a space and the variant's option1 (which should be colour) to it. Don't forget the aria attr.
Append the variant ID to the product URL.
Use that snippet in the main grid loop instead of the product-card snippet.
This gets you 75% of the way there - there'll be more to do, of course, but that's the basics.
Outputting this: <!-- {{ product_card_variant | json }} --> in your new can be helpful to demystify the data in the variant object.
No app needed, no $$$$ needed, no need to sit through several minutes of video the entire purpose of which is to get you to buy the solution: just a previous community answer and a bit of experimentation in the code.
I hope this helps someone else.
G
