Use an aluminum spike and plastic ferrule to anchor the gutter to the fascia. Nailed through the face of the gutter, the head of the spike is color matched. Sold as a 2-piece set, spike and ferrule is typically installed every 2 ft. to 3 ft based on climate.
Nail spike through the gutter using the ferrule to keep the gutter from being compressed. Pre-drilling the gutter is recommended for a clean installation.