I was R031 and still a CV3. I was born this way  and nothing can be done to change it.
The colour vision rating  is more of a safety thing for yourself and the troops around you.
Colour codes on arty  rounds, gernades etc for quick visual ID. No one wants to fire the wrong round on target or wrong colour smoke etc. 
There are trades that are closed to you  when you  are CV 3 but does not mean the end of a career in the army. Have the recruiting staff go over your vision rating and see what  trades are still open to you.
The book test is not as correct as the more advance tests,  the book is just gives a general idea of what  colours are affected by your vision, then you have the coloured disk test, put the pucks in the order of shade from one colour to  the next.  I failed the book tests ( was tested using 3 differerent test books to narrow down the colour problems, ) then I did the disk test and faile dit, but they  rated me Cv2 for my  personal safety, when on a call out at  LFCA HQ I arranged to get a Latern test  at DCIEM the same test they  give pilots and i failed it badly was given the final CV3 rating for my  personal safety.
There are many  trades open to people who areCV3, just be prepared to look at a few other trades. Mostly  likely  you  will find  the following trade areas closed to you, most aircrew trade, naval hard sea trades, some tech trades,  and some others. I remustered to Fin Clk  now a closed trade but tht  had nothing to do with me being colopur blind, just a choice.  Still a lot of interesting trades left to you