Photo Filter is photo editing software that puts a layer of color on top of any photo you create. Unlike other photo filters that adjust the photo with color types to make it look old, bright, sepia, etc., Photo Filter Free only places a predesigned layer of color that only makes the photo less visible.
One thing that Photo Filter has in its favor is color. Nearly every filter in the program is colorful, with rainbows, rainbow-colored bricks, bright lights, and more. But rather than alter the photo, the filter simply places a semi-transparent color layer on top of the photo so that the photo is faded into the background of that layer. It has no other editing features. You can also place multiple layers on top of each photo, but after the first layer the photos become much harder to see. You also can't go back to old layers if you need to. You have to undo all of the layers and start from scratch.
Few photo filtering apps add colors these days, but Photo Filter isn't the right way to add color. It essentially blocks a photo for no real benefit, and without added tools to enhance your images, combine filter layers, or undo any one action, it is harder to use than strictly necessary. If built upon and expanded with new editing tools and features, Photo Filter Free could be a solid free editing tool; but for now, it offers minimal benefits.