“Until EOL” is easy: DELIMITERn open = :, close = ((EOL))
Unfortunately, stop-on-other-whitespace is harder; not sure how it could be done natively in a Notepad++ UDL.
There are two alternatives that I can think of:
just define it as a delimiter with ((EOL)) closing it, but set the STYLE for that delimiter to allow nesting of anything else (that you have defined). For example, if = was defined in
Operators 2 as magenta,
Number defined with blue foreground and cyan background,
Keywords 1 defined as Green/Bold with Area as the keyword, and
DELIMITER1 defined with open = :, close = ((EOL)) and foreground=red, bg=yellow, nesting=operators2+numbers, I see:
7f97a779-14f3-4046-b719-3abb641fdf54-image.png
which might be enough for you.
Otherwise, you can add extra highlighting to a UDL language using regexes via the script EnhanceUDLLexer.py that
@Ekopalypse shares
in this linked post