This is [The Long Result][1] by John Brunner. There are a [number of elements][2] that match your description; 

 - Planet called Starhome - **Check.**
 - Aliens called *'Relgans*(?)' - **Check** (Re**gul**ans, actually)
 - Book cover with rocket - **Check**
 - Blue aliens - **Check**
 - Legs that bend the wrong way - **Check** (described as "back-bent")
 - Anti-hol - **Check** (described as "Anti-Alcohol")

[![enter image description here][3]][3]


  [1]: http://www.goodreads.com/book/show/2881664-the-long-result
  [2]: https://books.google.co.uk/books?id=ZFKRaKfwg4wC&pg=PT141&lpg=PT141&dq=Long%20Result%20By%20John%20Brunner%20%22blue%22&source=bl&ots=OTfbjt4oWI&sig=VWWdZEvcKSM5cB5Kgf6RaYEw_qE&hl=en&sa=X&redir_esc=y#v=onepage&q=Long%20Result%20By%20John%20Brunner%20%22blue%22&f=false
  [3]: https://i.sstatic.net/SRA1W.jpg