Update: Plurk CSS code to create a bigger box for inputting reponses. Adding a "background:" will allow you to color the text box.

http://www.colchis.com/clrtable.html color table

Add the following line to you current CSS code for the #input_small code:

background:#A7CEE8;



/* make a bigger input box for the responses */
#input_small {
height: 75px;
background:#A7CEE8;
}