01
A color name is not a specification
Terms such as black, gray, green, purple or red cover broad ranges. Identify the quarry and product because surface texture, shade, inclusions and weathering can differ even within the same general color family.
02
Review dry, wet and aged appearances
Slate often darkens when wet, and weathering products may develop buff, tan, brown or other tones over time. Recent samples cannot fully represent decades of exposure, so use documented older projects from the same product when available.
03
Plan blends mathematically and visually
Define percentages, distribution and any intentional pattern. Approve a sufficiently large mockup and require installers to draw from multiple containers so the roof does not develop accidental blocks or stripes.