Unfortunately, for now, there is no option in the shortcode to change that text, but the following code should help you with that:
(Insert it in “Custom jQuery Footer” text-field located in Customizing ▸ General ▸ Extra menu)
jQuery(".tv_color_box div a.button").html(jQuery(".tv_color_box div a.button").html().replace("Read More", "Your Text"));
Replace “Your Text” with text as you wish.
If this solution does not work for you, please provide me with an address to your website.