Rewrite rule to prevent apache decoding url before htaccess?

We have a htaccess rule like this:

RewriteRule ^(.*)/(.*)/(.*) ../app$1/scripts/api/index.php?fn=$2&$3 [L]

This works fine in most cases, however, Apache is decoding the url before it arrives at this rule, so a url like beta/list/&cat=red%20%26%20blue, is seen by htaccess as beta/list/&cat=red & blue so we get cat='red' and blue=null coming into index.php instead of cat='red & blue'.

I've read that the workaround for this issue is to use server variables like %{REQUEST_URI} %{THE_REQUEST} in the htaccess rule as these are not decoded before use, but it's difficult to implement. The question mark in the RewriteRule makes everything go crazy and I can't figure out how to escape it.

Can any experts out there fix this rule to behave like the one above?

RewriteCond %{REQUEST_URI} ^(.*)/(.*)/(.*)
RewriteRule . ../app%1/scripts/api/index.php?fn=%2&%3 [L]

from Rewrite rule to prevent apache decoding url before htaccess?