Is it slate? It looks like a concrete tile. Slate usually has variety of colors. Just use more GW or roof snot to improve cling, and test a small area.
If it isnt slate it is a faux slate. The red color on the upper section is that algae or is it iron oxide seeping from those slate shingles. I wonder because it looks like the red is limited to that batch only which would mean it may be real slate. All natural slate contains iron. Some more than others and it is not uncommon for a batching effect to happen where these 100 square feet of slate has iron on it and the next 100 square feet doesn't, even on the same roof.