This is the standard css styling for the color around the icon:
.header-title .fa,
.header-title .main-title-img{
box-shadow: 0px 0px 0px 3px rgba(255,255,255,0.45);
}It uses rgba color so rgba(255,255,255,0.45) is white with a 0.45 opacity so that it appears to let the background color through slightly and with a lighter shade.
change the rgba(255,255,255,0.45) part to any color
as well as rgba the color can be defined as rgb or hexadecimal
e.g. rgba(11,72,158,1), rgb(11,72,158) and #0b489e are all the same blue color.