The Channel Blur effect individually blurs the red, green, blue, or alpha channels of a layer.
There is some cool things you can do with this blur.
You can blur only specific channels, and if you keep all the numbers the same for each channel, you will get a balanced blur.
Note: If you have noise or artifacts primarily in one color channel—such as MPEG compression artifacts in the blue channel of DV footage—use Channel Blur to clean up the noise in that channel, leaving the other channels sharp.This effect works with 8-bpc, 16-bpc, and 32-bpc color.
(From Adobe Help Site) https://helpx.adobe.com/after-effects/using/blur-sharpen-effects.html#channel_blur_effect