How to make each 'card' on my page a different color?

Site URL: https://www.maeskeller.com/projects

Hello,

I'm an illustrator using Squarespace for my portfolio website, and I had a question that I was hoping to find assistance with.

On my site I plan to have a list of completed 'projects' for people to view. I wanted to organize these projects in 'card' layouts, with each card being a different color as you scroll down. However, Squarespace does not seem to allow me to change the background color of individual cards. When I try to change the color, it changes both the projects being shown on the page, rather than just the one. Is there a way to individually customize each image block so that my cards are different colors? 

Attaching a screenshot so that people can see what I'm talking about. Thank you!

Add to Design > Custom CSS

/* Mary Tales */
div#block-yui_3_17_2_1_1609195466824_3817 .image-card-wrapper {
    background: red !important;
}

div#block...3817 is block id. Use this tool to find block id. https://chrome.google.com/webstore/detail/squarespace-id-finder/igjamfnifnkmecjidfbdipieoaeghcff?hl=en