If the ecard that you are trying to send has a dark background, your message will sometimes default to black when previewed.
Please highlight the message you have typed. Click on the text color box at the top of the personalization box and select the color that you would like to have your text to appear in, even if the color you would like to use is white. The text will now appear in the color you have chosen.
Now when you preview your ecard the message should now appear!