I want to achieve this kind of colouring effect using Adobe Illustrator/Photoshop.
The noise/grain looks computer-generated.
I have tried to use Texture > Grain and adjusting but the result looks quite different.
How can I create that effect using Adobe Illustrator? If it is not possible on Illustrator, how do I do it on Photoshop?
The grain effect in Illustrator doesn't allow a lot of control when applying it. In my opinion, Photoshop can make a much better job of it.
An easy way is to apply Film Grain in the FX tab in the Adobe Camera RAW filter. You need to make sure you apply it on a Smart Object to get the Adobe Camera RAW filter to work as a Smart Filter.
Another method would be to do it manually, by adding a layer above the artwrork, fill it 50% grey, and apply the noise filter, and then change the layer blending mode and opacity to get the look you want. It's also possible to scale the layer to make the grain larger, or apply a very slight gaussian blur to soften the effect.
When I have to use Illustrator effects, I usually duplicate the artwork twice. I then apply a grain filter to one copy that converts the image to black and white, such as stipple. Then I use this black and white layer as a mask for the second copy. This allows for finer control over the colors, since you can change the grain color on a shape by shape basis, and make it as strong or as subtle as you want.
However, that works better on simple art. What might be easier is to take the art into photoshop, create a black and white grain layer, then blur it slightly, then use the Overlay transfer mode.
