Velvet and suede have a raised pile that traps light between the fibres rather than reflecting it straight back, which makes the same dye colour read noticeably darker and richer than it would on a flat weave.

Practical advice
Expect a velvet or suede garment to look deeper than its own colour swatch suggests — this is a genuine property of the fabric's texture, not a colour-matching error.
Always confirm with the physical garment under real light before committing to a colour choice — see methodology.