First install epel repository  
#yum install epel-release

Install shellinabox by below command

#yum install shellinabox

The shellinabox config file is located in /etc/default/shellinabox file by default in Debian/Ubuntu systems. In RHEL/CentOS/Fedora, the default location of config file is /etc/sysconfig/shellinaboxd.

To change web terminal color scheme to white on black follow the following steps

#vim /etc/sysconfig/shellinaboxd
 comment below line
 OPTS="--disable-ssl-menu -s /:LOGIN"

uncomment below line
 OPTS="--user-css Normal:+black-on-white.css,Reverse:-white-on-black.css --disable-ssl-menu -s /:LOGIN"

This enables right change in profile on right click on browser.

restart the service

note* sometimes the white-on-black.css is not installed. then service will not restart/start and will give error

workaround :

cd /usr/share/shellinabox/

#cp black-on-white.css white-on-black.css
#sed -i s/ffffff/111111/g white-on-black.css
#sed -i s/000000/ffffff/g white-on-black.css
#sed -i s/111111/000000/g white-on-black.css

now restart the service.

(you can change colours by changing the hex colour code in css.)

now for web terminal open a link

https://ip-address:4200 (default port is 4200 you can change it to any by editing config file i.e. /etc/sysconfig/shellinaboxd)