This is in emacs 26.1 on CentOS 7.5
Keywords don't seem to be identified as such and therefore don't seem to be coloured as they should be. I've installed ada-mode through emacs. Putting the cursor over one and typic C-u C-x = doens't indicate that it's a keyword; function names are identified as such as are comments and constants.
The only other bit of info that may be relevant is that I have compiled emacs myself as the one on CentOS is ancient.
Hope this is enough to work out how to fix this -- apologies in advance if it isn't.
Jonty