Purple "dot" .. what could it be?

[cjacek]

I wasn't sure where best to post this so hopefully it's not off topic... I've been handed a beautiful condition Sony LCD projector with 2000 hrs on it, basically free of charge. It's the model number VPL-HS20. Not a scratch on it and very well taken care of by the previous owner. I've been testing it (before I get a proper screen) on a white cardboard sheet (ignore the folding mark). I have attached a few photos. Excuse the quality of my camera 'cause the actual picture from the projector is beautiful "cinema like" but it has an issue... See if you can spot a purple "dot" in the same place. The previous owner mentioned that he never had this problem before. I am hoping it's a simple fix like maybe cleaning something or replacing a filter etc.... I'd really appreciate your help with this. Thanks in advance.