Open your item db, scroll down to this line
12221,Megaphone_,Megaphone,2,2,,10,,,,,0xFFFFFFFF,63,2,,,,,,{ input @megaphone$; announce strcharinfo(0) + ": " + @megaphone$,bc_all,0xFF0000; end; },{},{}
Changed it's color by changing this color hex 0xFF0000 to something that you like,
Use this site if you need assistant
http://www.colorhexa.com/