The Mix textures are used for mixing two textures together (either linearly or according to a cosine wave).
In the next example an RGB Image Texture is mixed with a RGB Color using different settings for the amount. The first material shows the regular RGB Image, because Greyscale Texture is used for the amount and set to 0.0. The second material shows the same RGB Image Texture passing through the Mix Texture with the amount set to 0.5. Sliding the Amount to 1.0 will result in full yellow color.
The third material has a Saw Wave Texture and the fourth material has a Noise Texture used for the amount.
