HTML validation complains about CSS parse error

After updating the plugins and WP core, I noticed the plugin is outputting CSS that HTML validation and code editor is complaining about. Essentially, when there is no value, blank CSS values are output like this (see color: !important parts below):

.sfsi_subscribe_Popinner input[type=email]::-webkit-input-placeholder {
    font-family: Helvetica, Arial, sans-serif !important;
    font-style: normal !important;
    color: !important;
    font-size: 14px !important;
    text-align: center !important;
}

.sfsi_subscribe_Popinner input[type=email]:-moz-placeholder {
    /* Firefox 18- */
    font-family: Helvetica, Arial, sans-serif !important;
    font-style: normal !important;
    color: !important;
    font-size: 14px !important;
    text-align: center !important;
}

.sfsi_subscribe_Popinner input[type=email]::-moz-placeholder {
    /* Firefox 19+ */
    font-family: Helvetica, Arial, sans-serif !important;
    font-style: normal !important;
    color: !important;
    font-size: 14px !important;
    text-align: center !important;
}

.sfsi_subscribe_Popinner input[type=email]:-ms-input-placeholder {
    font-family: Helvetica, Arial, sans-serif !important;
    font-style: normal !important;
    color: !important;
    font-size: 14px !important;
    text-align: center !important;
}

HTML validation complaint:
Error:?CSS:?color: Parse Error.

Code editor complaint:
Term expected