デフォルトとスキーマの色に基づいて、これを一緒にハックすることができました。
.ui-datepicker .ui-state-highlight {
border: 1px solid #d3d3d3;
background: #e6e6e6;
color: #363636;}
.ui-datepicker .ui-state-active {
border: 1px solid #aaaaaa;
background: #518bdf url(images/ui-bg_glass_65_518bdf_1x400.png) 50% 50% repeat-x;
font-weight: normal;
color: #fff;
outline: none;}
$.datepicker._gotoToday = function (id) {
var inst = this._getInst($(id)[0]),
$dp = inst.dpDiv;
this._base_gotoToday(id);
var tp_inst = this._get(inst, 'timepicker');
now = new Date();
var now_utc = new Date(now.getUTCFullYear(), now.getUTCMonth(), now.getUTCDate(), now.getUTCHours(), now.getUTCMinutes(), now.getUTCSeconds());
this._setTime(inst, now_utc);
$('.datetime:focus').datepicker('setDate', now_utc);
// $('.ui-datepicker-today', $dp).click();
};