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.