Reviews that are pinned have a data-pinned
attribute added to them, so you can target them with CSS and style however you like.
Here is an example:
.glsr-review[data-pinned] {
position: relative;
}
.glsr-review[data-pinned]::before {
background: red; /* Change the color of the icon here */
position: absolute;
content: '';
display: block;
width: 24px;
height: 24px;
top: 0;
left: 0;
mask-image: url("data:image/svg+xml,%3Csvg xmlns='https://www.w3.org/2000/svg' viewBox='0 0 20 20'%3E%3Cpath d='M5 3.61V1.04l8.99-.01-.01 2.58c-1.22.26-2.16 1.35-2.16 2.67v.5c.01 1.31.93 2.4 2.17 2.66l-.01 2.58h-3.41l-.01 2.57c0 .6-.47 4.41-1.06 4.41-.6 0-1.08-3.81-1.08-4.41v-2.56L5 12.02l.01-2.58c1.23-.25 2.15-1.35 2.15-2.66v-.5c0-1.31-.92-2.41-2.16-2.67z'/%3E%3C/svg%3E");
z-index: 1;
}