The Blend Shaders package contains over 20 shaders for blending textures and sprites in Unity (based on Photoshop's blend modes), and it contains a cginc file with a standalone function for each of the blend modes.

• Add
• Average
• Color Burn
• Color Dodge
• Darken
• Difference
• Exclusion
• Glow
• Hard Light
• Hard Mix
• Lighten
• Linear Dodge
• Linear Light
• Multiply
• Negation
• Overlay
• Phoenix
• Pin Light
• Reflect
• Screen
• Soft Light
• Subtract
• Vivid Light

Use the Unity Package Manager to install the Blend Shaders package.

1. Open the Package Manager in Window > Package Manager
2. Click the add (+) button in the status bar
3. Select Add package from git URL from the add menu
4. Enter the following Git URL in the text box and click Add:

https://github.com/zigurous/unity-blend-shaders.git