So (I have phpstorm, but it should work):
1. settings -> file types -> recognized file types
Create a new language inside keywords -> add -> [this gap]
2. In the registered patterns below prescribes the desired file types. Here is the trick: if you set the type, he will offer to migrate an existing pattern. So if, for example, need *.php, prescription *.ph? or.php* (the same for your extensions)
3. go to editor -> colors & fonts -> custom, there is keyword1, he write back.