Guard hairs are hairs that grow longer than the rest of their coat and are coarse.
The sire is lighter, it is rare poodles stay that deep dark brown puppy color. My Bea started her color change around 8 months in earnest at 18 months but it took 3 years to fully lighten.
Besides the red and apricot family of colors, brown seems to be a color that almost always fades a lot as poodles grow up. True dark brown poodles aren’t very common. Seeing that you’re already seeing lighter hairs at 8 months in that quantity, it is almost certain your sweet boy will lighten. I think it becomes most apparent by age 2, and by age 5 you’ll see the true color he’ll lighten to. He might ending up having lots of different shades of brown. If he has lots of blacks in his pedigree, it helps a bit to hold some of the darker color. I am confident that in time you will grow to LOVE whatever color he becomes.