Determines how sprites/animations should blend with the background. The possible values are listed below.
Note that in most of Factorio it is assumed colors are in alpha pre-multiplied format, see FFF #172 - Blending and Rendering. Sprites get pre-multiplied when loaded, unless premul_alpha is set to false on the sprite/animation itself. Since generating mipmaps doesn't respect premul_alpha, lower mipmap levels will be in pre-multiplied format regardless.
"normal" | "additive" | "additive-soft" | "multiplicative" | "multiplicative-with-alpha" | "overwrite"