Vuforia Augmented Reality ( Change image target Color )

Hi, Only for usd15 is the budget for this solution. No more than this. I would like someone to teach me how to change certain image viewed by augmented reality apps from mobile phone camera to grayscale. For example when the image target been scanned by mobile phone the 3d model will show up and i want the image target on the paper viewed by the mobile phone turn to grayscale. As you can see the camera show the paper with colored deer. I want unity to change the colored of the deer in the mobile camera view as grayscale. The augmented reality is using vuforia and unity. my method for now is using plane that are unrealistic because the cards on the mobile view looks so plain not real... any method like adding something like layer on top of the image target to blur or grayscale it... as the attach...i need the lion image turned grayscale or blurred making the lion to stand out...