york template - background colors of index page tiles

Hi,

When I'm adding new tiles to my portfolio (using the York template), the background color of the image is usually applied to the entire responsive tile.  For some reason, when I add new images, it's assigning a lighter tint of the color (making the edge of the image obvious & not seamless. (screenshot attached).  

How is that background color getting assigned? Any ideas why new ones that I add are not seamless like my 6 existing portfolio items (& the York demo site)?

Thanks for any insight!

Hi,

What is site url? We can check easier