When using slack with GitHub, is there any option to send messages by checking labels. For example if in commit exists label "design", message will go to 'design' channel. Is there any ready implementation or we need to do something custom?
No, not yet (May 2018, a year after the OP's question)
This is still pending in integrations/slack issue 384
I'm a member of a Slack channel dedicated to a specific feature of a repo that covers a wide variety of features. Right now we have an internal Hubot to filter down to a specific label and then post messages to the channel.
It'd be cool if this official integration could replace our internal by allow subscribing to only issues/PRs that have a specific label instead of the entire repo.
So it is technically possible, but for now through the use of an external third-party bot.