Can I change this ?

[NomanProdhan]

I use MyAlert Plugin. But I don't like the Alert's background color which is appear at the top of my forum. Can I change it ?

I am sorry for my bad English. I give a screenshots below - - -
   

[.m.]

you have to modify background colors & text color used in alerts.css belonging to active theme of the forum

[Bala]

This user has been denied support.

There is my alerts wrapper class in alerts.css. Alerts.css is located in your Themes and templetes->your theme name.
Change the background to any hex value

ie background: #ebebeb;
I have done this to my own alerts as I wanted a black background.