@okereke-divine,

You can use the CSS code below:

#wpdcom .wc-field-submit input[type="submit"] {
   color: #ff4d4d !important;
}

Put the code in the Top Admin Bar > Customize > Additional CSS > "Additional CSS" textarea, save it, delete all caches and check again. 

The red marked value can be changed as you like. 

Please don't forget to press Ctrl+F5 (twice) on the frontend before checking.

Thanks. It worked