Custom triggers - how to create and edit them

So there's this trigger I'm dealing with for a pick many/images slide and it's change state of [image] to Answered - 'Answered' being a custom trigger. 

 

Unfortunately, there's a problem with said trigger on the course I'm writing - namely that the 'answered' state involves a highlighting colour that's too pale to be fit for purpose in this instance. Therefore, I'd like to change the highlighting colour. However, I don't know how to edit this trigger and would like your help. The trigger was created by a very secretive, reticent former colleague of mine who left ages ago so I can't really ask him, but it can't have been impossible to have been created in the first place; something must be hidden somewhere that I'm not seeing, it's just a question of where and probably also how. 

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