Display the thumbnails smaller. Requires adding the class 'color-only' to the Layer

smaller-colors-thumbnails.css

.mkl_pc .mkl_pc_container .mkl_pc_toolbar section.choices > ul > li.color-only .choices-list li {
    box-shadow: none;
    width: 11%;
}

.mkl_pc .mkl_pc_container .mkl_pc_toolbar section.choices > ul > li.color-only .choices-list li button span.choice-text {
    position: absolute;
    top: 100%;
    left: 50%;
    transform: translateX(-50%);
    min-width: 80px;
    padding: 3px;
    border-radius: 4px;
    z-index: 3;
    background: #FFF;
    box-shadow: 0px 5px 12px rgb(0 0 0 / 13%);
    display: none;
}
.mkl_pc .mkl_pc_container .mkl_pc_toolbar section.choices > ul > li.color-only .choices-list li button:hover span.choice-text,
.mkl_pc .mkl_pc_container .mkl_pc_toolbar section.choices > ul > li.color-only .choices-list li button:active span.choice-text,
.mkl_pc .mkl_pc_container .mkl_pc_toolbar section.choices > ul > li.color-only .choices-list li button:focus span.choice-text {
    display: block
}


.mkl_pc .mkl_pc_container .mkl_pc_toolbar section.choices > ul > li.color-only .choices-list li i.mkl-pc-thumbnail {
    max-width: 100%;
    max-height: 100%;
    height: 28px;
    margin-bottom: .2em;
}
@media (max-width: 660px) {
  .mkl_pc .mkl_pc_container .mkl_pc_toolbar section.choices > ul > li.color-only .choices-list li button i.mkl-pc-thumbnail {
      padding-bottom: 100%;
  }
}