I was looking to add color swatches and make my size selectors grey out / cross out if the selection isn't available,
This seems to be easy enough on regular themes but I'm struggling to make it happen with the symmetry theme and apps don't work because the theme has a option selector in the collections page,
Any help is greatly appreciated, thanks
I completely understand what it is that you are going for. When it comes to color swatches I recommend getting an app like Swatches, Swatchify, or Quick View and Color Swatches.
You said, however, that you are having troubles with an app. Are you getting any errors or is it just not looking/working the way that you would like it to?
For the greying out of the size selectors feature you would definitely need to do some code adjustments for that. The only thing that will be greyed out at the moment with that theme would be the out of stock option when your customers would go to add it to the cart.
Unfortunately, when it comes to themes that aren't created by Shopify we aren't able to dig into the nitty gritty of the theme code. For that, it would be best to reach out to the theme developer, Clean Themes, as they will have the best knowledge about the layout of their themes code. This link here is actually their support email. If you contact that email they should get back to you with the next best steps on how to set that up.
Another option would be to go to the Shopify Experts. They should also be able to help you get that setup.
I hope that was able to help you! Please let me know what issue you are having with the apps and what apps you are using and I may be able to help further with that as well.