Lets say we have a 3 Channel (RGB) image given by some matrix A
A = [[[198 218 227] [196 216 225] [196 214 224] ... ... [185 201 217] [176 192 208] [162 178 194]]
and a blur kernal as
K = [[0.1111, 0.1111, 0.1111], [0.1111, 0.1111, 0.1111], [0.1111, 0.1111, 0.1111]] #which is actually 0.111 ~= 1/9
The convolution can be represented as shown in the image below
As you can see in the image, each channel is individually convoluted and then combined to form a pixel.