I found the W-H lantern test to be easy to pass (got 100%) while the Isihara Plates were extremely hard.
It is also apparent that one could practice for the W-H by buying some coloured LEDs and some switches
I did actually do that but never got around to putting them together by the time I went for the test...
I think Flyin'Dutch''s post above is very significant...
Historically, thousands of wannabee airline pilots went to the outlying bits of Europe (Hungary was popular) to get the initial CV test done. In fact any ICAO contracting state would have done the job. This is unsuprising because if e.g. you fail the W-H test, you can never re-take it in the rest of your life, so if you think you are marginal and might pass it on a "good day" then the last thing you want to do is to do the initial one at say Gatwick
The FAA route is no longer useful because EASA FCL requires (2014 onwards) that if the "operator" is EU based (see the other thread) you need the EASA pilot papers and an EASA medical as well. I imagine some pilots who can get only FAA medicals will be able to continue flying by sorting out a non EU residence, which is obviously easy if you don't mind living somewhere where it rains rather a lot
Sadly, Croatia is not a good plan...
The CAA used to offer a concession to ICAO CPL/ATPL holders with ICAO Class 1s but I have no idea if they still do this.