Hi!
There is no direct way to remove only standard community. The correct way of achieving is what you are already trying, using regex match condition. You need to sort more details what all communities are being received in your environment and come up with a match condition that solves your purpose.
How about below community for invert-match?
show policy-options community test
invert-match;
members *:*:*;
Below link displays some examples and regex operators that could be useful to you..