The Blend effect blends two clips using one of five modes. After you blend clips using this effect, disable the clip you selected from the Blend With Layer menu by selecting the clip and choosing Clip > Enable.
Color Only colorizes each pixel in the original image based on the color of each corresponding pixel in the secondary image.
Tint Only is similar to Color Only but tints pixels in the original image only if they are already colored.
Darken Only darkens each pixel in the original image that is lighter than the corresponding pixel in the secondary image.
Lighten Only lightens each pixel in the original image that is darker than the corresponding pixel in the secondary image.
Crossfade fades the original image out while the secondary image fades in.