Relative color syntax

Trying to invert a sRGB color using the relative color syntax from CSS Color Module Level 5:

Syntax Expected Result
rgb(from #ff6600 calc(100% - r) calc(100% - g) calc(100% - b))
rgb(from #ff6600 calc(255 - r) calc(255 - g) calc(255 - b))
rgb(from #ff6600 calc(1 - r) calc(1 - g) calc(1 - b))