Takayuki Miyoshi on "[Plugin: Contact Form 7] Question about the text box"

Open the CSS stylesheet in your theme and move to line 192, then you can find this:

input[type="text"], textarea {
    background: none repeat scroll 0 0 #EAEAEA;
    color: #8D8C8C;
}

Then change it to:

input[type="text"], input[type="email"], textarea {
    background: none repeat scroll 0 0 #EAEAEA;
    color: #8D8C8C;
}

It's basic CSS. If you are not familiar with CSS, you can learn it with these websites.

• Learning CSS – W3C
• CSS Tutorial – W3Schools
• Learn CSS | MDN – Mozilla Developer Network
• CSS Basics