Post grid hover color

You can use the built-in customizers in the ‘Style’ tab of the element in the editor to change the border-bottom color. I see that you have already done the same.

For changing the color of the background on image hover, you can try using pseudo elements for the IMG element as explained here with various examples –

https://bryanlrobinson.com/blog/how-to-css-after-elements-for-background-overlays/

I tried the below custom CSS and it worked –

/* Disable current hover */
.lae-portfolio-wrap .lae-portfolio .lae-portfolio-item .lae-project-image:hover img {
    -webkit-filter: brightness(100%);
    filter: brightness(100%);
}

.lae-portfolio-wrap .lae-portfolio .lae-portfolio-item .lae-project-image:hover:before {
    content: "";
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-image: linear-gradient(120deg, #eaee44, #33d0ff);
    opacity: .7;
    z-index: 1;
}

.lae-portfolio-wrap .lae-portfolio .lae-portfolio-item .lae-project-image .lae-entry-info {
    z-index: 100;
}