* krilla: CMYK, gray and spot colors keep their exact inks (patch 17)
Gray, CMYK, Separation and DeviceN colors stored each component as a
u8, so every ink was written as a multiple of 1/255: C75 became
0.7490196 and C4 M4 Y4 K4 became 0.039215688.
- cmyk, luma, separation and device_n Color::new_f32 take components
from 0 to 1 and write them as given. The u8 constructors are
unchanged.
- Gradient stops rewritten into one DeviceN, Separation or CMYK space
keep their components.
- Mesh gradients write corner colors at 16 bits a component.
* Tests: the 75% K mesh corner comment gives the asserted 0.749996