- Member synfig::Color::BLEND_ALPHA_BRIGHTEN
- If A is less opaque than B, use A
- Member synfig::Color::BLEND_ALPHA_DARKEN
- If A is more opaque than B, use B
- Member synfig::Color::BLEND_ALPHA_OVER
- multiply alphas and then straight blends using the amount
- Member synfig::Color::BLEND_STRAIGHT_ONTO
