I'm using the red slots on my Hero VII and no problems getting ram to 2800. Some folks have had issues with the red slots and switched to the black ones and ran what they expected. Would say try the reds and if they work how you like them leave em, if not switch em out.
AMD 2700X, Asus ROG Strix X470-F, G.Skill Trident Z Neo 3600 (16gbx2), XFX RX 580, NZXT Kraken X62, Corsair 750D, SeaSonic 860W, OCZ RD400, Samsung 950 Pro 256Gb, Intel 520 120Gb SSD