Download the WhatsApp Plus Blue on your phone and then run the apk file to install it,
all the applications that are not updated from the play store when it is been started the system will requests from you allowing for the unknown sources to be installed ,
put true mark in the setting for this choice and get out from it so it the application will be installed.
WhatsApp Plus Blue Download Link APK
WhatsApp Plus Blue Download Link 2 APK