The Blend variable controls how the selected instance combines its colors with whatever is drawn before. The final appearance of a Sprite or NineSlice depends on its Blend, Alpha, Source File, and Color values.
Normal Blend is the default value. When an instance uses Normal Blend, it interpolates its color with whatever it draws on top of using its Alpha value as a weight.
If a Normal Blend Sprite has an Alpha of 255, then the Sprite completely replaces whatever it is drawn on top of.
If a Sprite has an alpha of 128 (roughly half of 255), then it averages its color with whatever it is drawn on top of.
A Sprite with 25 alpha (roughly 10%) will blend with whatever it is drawn on top of, but its color is given a weight of roughly 10%.
The examples above use the Alpha value to apply transparency. Note that if the source file (.png) has transparency as part of the file, the same effect applies.
Additive Blend results in the color of a Sprite being added to whatever it is drawn on top of. This typically results in the Sprite or NineSlice making things brighter. Additive Blend can be used to simulate a light.
Since Additive Blend results in a modification of what is under instead of a replacement, an Additive Blend Sprite or NineSlice typically appear transparent even when Alpha 255.
As alpha is reduced, the brightening effect is reduced. A Sprite or NineSlice with an alpha of 128 only applies roughly half as much of a brightening effect.
A Sprite or NineSlice with an alpha of 25 applies a slight brightening effect.
Stacking multiple Sprites or NineSlices with an Additive Blend results in the brightening effect stacking as well.
Replace blend results in the Sprite or NineSlice completely replacing whatever it is drawn on top of regardless of Alpha or transparency in the source file.
A Sprite with no transparency in its source file drawn at 255 looks the same whether it uses Replace Blend or Normal Blend.
Changing the Alpha on a Sprite or NineSlice with Replace Blend does not affect how it is drawn - it is always drawn at full opacity.
Replace Blend results in a Sprite or NineSlice being fully opaque even if its source file has transparency. The following image shows two Sprites displaying the same image.
