I was able to figure it out! Here are some of the steps to take when doing this:
1. Place both images under a link block
2. Grey icon set to position: absolute, overflow: hidden AND hover state set at opacity of 0%
3. Gold hover icon set to position: auto, overflow: visible AND hover state set at opacity of 0%
The transition upon hover can be placed on the grey icon for a smooth hover effect (I used opacity 200 ms ease).
Heres a screenshot of how it's structured. sm-row class is just a link block, Image 10 is the grey icon, Image 9 is the gold icon:
Thanks for leading me in the right direction!