An imaging system may include an image sensor having an array of pixels. The image sensor may include an array of microlenses formed over a substrate and an array of color filter elements interposed between the microlenses and the substrate. Dielectric wall structures may be interposed between the color filter elements. Light shield structures may be formed within or on the dielectric wall structures and may be used to reduce optical crosstalk between adjacent pixels. The light shield structures may be formed on opposing sides or corners of the color filter elements and may partially or fully extend along the height of the color filter elements. In some arrangements, the light shield structures may each have a vertical portion that contacts a side surface of an adjacent color filter element and a horizontal portion that contacts a lower surface of an adjacent color filter element.