How can I change the color of the subtotal and shipping cost? It is impossible to see on my form.

You can do it through CSS code injection: http://www.jotform.com/help/117-How-to-Inject-Custom-CSS-Codes

Try this code: 

.form-payment-subtotal form-payment-label,.form-payment-shipping form-payment-label{

    color: black !important;

}

Let us know if you need more help, we will be glad to assist you.