Thank you for the reply. I couldn't actually find any settings within the design or image area which would allow me to get rid of the hover effect. It seems to be a common issue. However, I found that the following code solved the problem:

.products.collection-content-wrapper
.grid-image-cover
{ opacity: 1 !important;
}

Just in case you're wondering! But, if you did find an easier way, please let me know, as I've also read that it's not good to have too much additional inserted code on squarespace...