I'm one of the believers in Mike not being every depiction of the Purple Guy in the series - e.g. in 4 I like to think Afton is the purple sprite whereas Michael is the brother. Given that Michael states that 'they' mistook him for his father, hence leading to his death in the spring suit, I personally believe that it makes sense for Afton to occasionally be represented as a purple sprite rather than a pink one - given that they apparently look so similar :v

(Though to be fair it seems like the children mistake everyone in existence for Afton lol)